diff --git a/Src/java/cql-to-elm-jackson/src/main/java/org/cqframework/cql/cq2elm/CqlTranslatorOptionsMapper.kt b/Src/java/cql-to-elm-jackson/src/main/java/org/cqframework/cql/cq2elm/CqlTranslatorOptionsMapper.kt
index 9b37e069a..3952b6673 100644
--- a/Src/java/cql-to-elm-jackson/src/main/java/org/cqframework/cql/cq2elm/CqlTranslatorOptionsMapper.kt
+++ b/Src/java/cql-to-elm-jackson/src/main/java/org/cqframework/cql/cq2elm/CqlTranslatorOptionsMapper.kt
@@ -22,9 +22,7 @@ object CqlTranslatorOptionsMapper {
             return fromReader(fr)
         } catch (@Suppress("SwallowedException") e: IOException) {
             @Suppress("TooGenericExceptionThrown")
-            throw RuntimeException(
-                String.format(Locale.US, "Errors occurred reading options: %s", e.message)
-            )
+            throw RuntimeException("Errors occurred reading options: ${e.message}", e)
         }
     }
 
@@ -34,9 +32,7 @@ object CqlTranslatorOptionsMapper {
             return om.readValue(reader, CqlTranslatorOptions::class.java)
         } catch (@Suppress("SwallowedException") e: IOException) {
             @Suppress("TooGenericExceptionThrown")
-            throw RuntimeException(
-                String.format(Locale.US, "Errors occurred reading options: %s", e.message)
-            )
+            throw RuntimeException("Errors occurred reading options: ${e.message}", e)
         }
     }
 
@@ -48,9 +44,7 @@ object CqlTranslatorOptionsMapper {
             toWriter(fw, options)
         } catch (@Suppress("SwallowedException") e: IOException) {
             @Suppress("TooGenericExceptionThrown")
-            throw RuntimeException(
-                String.format(Locale.US, "Errors occurred writing options: %s", e.message)
-            )
+            throw RuntimeException("Errors occurred writing options: ${e.message}", e)
         }
     }
 
@@ -61,9 +55,7 @@ object CqlTranslatorOptionsMapper {
             om.writeValue(writer, options)
         } catch (@Suppress("SwallowedException") e: IOException) {
             @Suppress("TooGenericExceptionThrown")
-            throw RuntimeException(
-                String.format(Locale.US, "Errors occurred writing options: %s", e.message)
-            )
+            throw RuntimeException("Errors occurred writing options: ${e.message}", e)
         }
     }
 }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CompilerOptions.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CompilerOptions.kt
index 3c3a98522..f2d807722 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CompilerOptions.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CompilerOptions.kt
@@ -38,7 +38,7 @@ object CompilerOptions {
 
     /**
      * Parses a string representing CQL compiler Options into an EnumSet. The string is expected to
-     * be a comma delimited list of values from the CqlCompiler.Options enumeration. For example
+     * be a comma-delimited list of values from the CqlCompiler.Options enumeration. For example
      * "EnableListPromotion, EnableListDemotion".
      *
      * @param compilerOptions the string to parse
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/Cql2ElmVisitor.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/Cql2ElmVisitor.kt
index e17ab01cd..14ddca105 100755
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/Cql2ElmVisitor.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/Cql2ElmVisitor.kt
@@ -73,6 +73,10 @@ class Cql2ElmVisitor(
         return null
     }
 
+    private inline fun <reified T> Any?.cast(): T {
+        return this as T
+    }
+
     override fun visitLibrary(ctx: LibraryContext): Any? {
         var lastResult: Any? = null
 
@@ -96,14 +100,13 @@ class Cql2ElmVisitor(
     }
 
     override fun visitLibraryDefinition(ctx: LibraryDefinitionContext): VersionedIdentifier {
-        val identifiers = visit(ctx.qualifiedIdentifier()) as MutableList<String>
+        val identifiers: MutableList<String> = visit(ctx.qualifiedIdentifier()).cast()
         val vid =
             of.createVersionedIdentifier()
                 .withId(identifiers.removeAt(identifiers.size - 1))
                 .withVersion(parseString(ctx.versionSpecifier()))
         if (identifiers.isNotEmpty()) {
-            vid.system =
-                libraryBuilder.resolveNamespaceUri(java.lang.String.join(".", identifiers), true)
+            vid.system = libraryBuilder.resolveNamespaceUri(identifiers.joinToString("."), true)
         } else if (libraryBuilder.namespaceInfo != null) {
             vid.system = libraryBuilder.namespaceInfo.uri
         }
@@ -112,13 +115,15 @@ class Cql2ElmVisitor(
     }
 
     override fun visitUsingDefinition(ctx: UsingDefinitionContext): UsingDef? {
-        val identifiers = visit(ctx.qualifiedIdentifier()) as MutableList<String>
+        val identifiers: MutableList<String> = visit(ctx.qualifiedIdentifier()).cast()
         val unqualifiedIdentifier: String = identifiers.removeAt(identifiers.size - 1)
         val namespaceName =
-            if (identifiers.isNotEmpty()) java.lang.String.join(".", identifiers)
-            else if (libraryBuilder.isWellKnownModelName(unqualifiedIdentifier)) null
-            else if (libraryBuilder.namespaceInfo != null) libraryBuilder.namespaceInfo.name
-            else null
+            when {
+                identifiers.isNotEmpty() -> java.lang.String.join(".", identifiers)
+                libraryBuilder.isWellKnownModelName(unqualifiedIdentifier) -> null
+                libraryBuilder.namespaceInfo != null -> libraryBuilder.namespaceInfo.name
+                else -> null
+            }
         var path: String? = null
         var modelNamespace: NamespaceInfo? = null
         if (namespaceName != null) {
@@ -132,12 +137,7 @@ class Cql2ElmVisitor(
             if (ctx.localIdentifier() == null) unqualifiedIdentifier
             else parseString(ctx.localIdentifier())!!
         require(localIdentifier == unqualifiedIdentifier) {
-            String.format(
-                Locale.US,
-                "Local identifiers for models must be the same as the name of the model in this release of the translator (Model %s, Called %s)",
-                unqualifiedIdentifier,
-                localIdentifier
-            )
+            "Local identifiers for models must be the same as the name of the model in this release of the translator (Model $unqualifiedIdentifier, Called $localIdentifier)"
         }
 
         // The model was already calculated by CqlPreprocessorVisitor
@@ -157,7 +157,7 @@ class Cql2ElmVisitor(
         return libraryBuilder.getModel(modelIdentifier, localIdentifier)
     }
 
-    private fun getLibraryPath(namespaceName: String?, unqualifiedIdentifier: String): String? {
+    private fun getLibraryPath(namespaceName: String?, unqualifiedIdentifier: String): String {
         if (namespaceName != null) {
             val namespaceUri = libraryBuilder.resolveNamespaceUri(namespaceName, true)
             return NamespaceManager.getPath(namespaceUri, unqualifiedIdentifier)
@@ -165,8 +165,8 @@ class Cql2ElmVisitor(
         return unqualifiedIdentifier
     }
 
-    override fun visitIncludeDefinition(ctx: IncludeDefinitionContext): Any? {
-        val identifiers = visit(ctx.qualifiedIdentifier()) as MutableList<String>
+    override fun visitIncludeDefinition(ctx: IncludeDefinitionContext): IncludeDef {
+        val identifiers: MutableList<String> = visit(ctx.qualifiedIdentifier()).cast()
         val unqualifiedIdentifier: String = identifiers.removeAt(identifiers.size - 1)
         var namespaceName =
             if (identifiers.isNotEmpty()) java.lang.String.join(".", identifiers)
@@ -191,10 +191,12 @@ class Cql2ElmVisitor(
         // with the namespace
         if (!libraryBuilder.canResolveLibrary(library)) {
             namespaceName =
-                if (identifiers.size > 0) java.lang.String.join(".", identifiers)
-                else if (libraryBuilder.isWellKnownLibraryName(unqualifiedIdentifier)) null
-                else if (libraryBuilder.namespaceInfo != null) libraryBuilder.namespaceInfo.name
-                else null
+                when {
+                    identifiers.isNotEmpty() -> java.lang.String.join(".", identifiers)
+                    libraryBuilder.isWellKnownLibraryName(unqualifiedIdentifier) -> null
+                    libraryBuilder.namespaceInfo != null -> libraryBuilder.namespaceInfo.name
+                    else -> null
+                }
             path = getLibraryPath(namespaceName, unqualifiedIdentifier)
             library =
                 of.createIncludeDef()
@@ -210,7 +212,7 @@ class Cql2ElmVisitor(
         return library
     }
 
-    override fun visitParameterDefinition(ctx: ParameterDefinitionContext): ParameterDef? {
+    override fun visitParameterDefinition(ctx: ParameterDefinitionContext): ParameterDef {
         val param =
             of.createParameterDef()
                 .withAccessLevel(parseAccessModifier(ctx.accessModifier()))
@@ -229,11 +231,7 @@ class Cql2ElmVisitor(
             }
         }
         requireNotNull(paramType) {
-            String.format(
-                Locale.US,
-                "Could not determine parameter type for parameter %s.",
-                param.name
-            )
+            "Could not determine parameter type for parameter ${param.name}."
         }
         param.resultType = paramType
         if (param.default != null) {
@@ -260,11 +258,7 @@ class Cql2ElmVisitor(
             "private" -> AccessModifier.PRIVATE
             else ->
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Unknown access modifier %s.",
-                        ctx.text.lowercase(Locale.getDefault())
-                    )
+                    "Unknown access modifier ${ctx.text.lowercase(Locale.getDefault())}."
                 )
         }
     }
@@ -275,7 +269,7 @@ class Cql2ElmVisitor(
                 .withAccessLevel(parseAccessModifier(ctx.accessModifier()))
                 .withName(parseString(ctx.identifier()))
                 .withId(parseString(ctx.codesystemId()))
-                .withVersion(parseString(ctx.versionSpecifier())) as CodeSystemDef
+                .withVersion(parseString(ctx.versionSpecifier()))
         if (libraryBuilder.isCompatibleWith("1.5")) {
             cs.resultType = libraryBuilder.resolveTypeName("System", "CodeSystem")
         } else {
@@ -296,14 +290,11 @@ class Cql2ElmVisitor(
         } else {
             def = libraryBuilder.resolveCodeSystemRef(name)
         }
-        requireNotNull(def) {
-            // ERROR:
-            String.format(Locale.US, "Could not resolve reference to code system %s.", name)
-        }
+        requireNotNull(def) { "Could not resolve reference to code system $name." }
         return of.createCodeSystemRef()
             .withLibraryName(libraryName)
             .withName(name)
-            .withResultType(def.resultType) as CodeSystemRef
+            .withResultType(def.resultType)
     }
 
     override fun visitCodeIdentifier(ctx: CodeIdentifierContext): CodeRef {
@@ -316,19 +307,17 @@ class Cql2ElmVisitor(
         } else {
             def = libraryBuilder.resolveCodeRef(name)
         }
-        if (def == null) {
+        requireNotNull(def) {
             // ERROR:
-            throw IllegalArgumentException(
-                String.format(Locale.US, "Could not resolve reference to code %s.", name)
-            )
+            "Could not resolve reference to code $name."
         }
         return of.createCodeRef()
             .withLibraryName(libraryName)
             .withName(name)
-            .withResultType(def.resultType) as CodeRef
+            .withResultType(def.resultType)
     }
 
-    override fun visitValuesetDefinition(ctx: ValuesetDefinitionContext): ValueSetDef? {
+    override fun visitValuesetDefinition(ctx: ValuesetDefinitionContext): ValueSetDef {
         val vs =
             of.createValueSetDef()
                 .withAccessLevel(parseAccessModifier(ctx.accessModifier()))
@@ -340,11 +329,7 @@ class Cql2ElmVisitor(
                 val cs =
                     visit(codesystem) as CodeSystemRef?
                         ?: throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Could not resolve reference to code system %s.",
-                                codesystem.text
-                            )
+                            "Could not resolve reference to code system ${codesystem.text}."
                         )
                 vs.codeSystem.add(cs)
             }
@@ -359,7 +344,7 @@ class Cql2ElmVisitor(
         return vs
     }
 
-    override fun visitCodeDefinition(ctx: CodeDefinitionContext): CodeDef? {
+    override fun visitCodeDefinition(ctx: CodeDefinitionContext): CodeDef {
         val cd =
             of.createCodeDef()
                 .withAccessLevel(parseAccessModifier(ctx.accessModifier()))
@@ -375,7 +360,7 @@ class Cql2ElmVisitor(
         return cd
     }
 
-    override fun visitConceptDefinition(ctx: ConceptDefinitionContext): ConceptDef? {
+    override fun visitConceptDefinition(ctx: ConceptDefinitionContext): ConceptDef {
         val cd =
             of.createConceptDef()
                 .withAccessLevel(parseAccessModifier(ctx.accessModifier()))
@@ -397,9 +382,7 @@ class Cql2ElmVisitor(
         val identifier =
             getTypeIdentifier(qualifiers, parseString(ctx.referentialOrTypeNameIdentifier())!!)
         val retrievedResult =
-            libraryBuilder.getNamedTypeSpecifierResult(
-                String.format(Locale.US, "%s:%s", modelIdentifier, identifier)
-            )
+            libraryBuilder.getNamedTypeSpecifierResult("$modelIdentifier:$identifier")
         if (retrievedResult != null) {
             return if (retrievedResult.hasError()) {
                 null
@@ -408,12 +391,7 @@ class Cql2ElmVisitor(
         val resultType =
             libraryBuilder.resolveTypeName(modelIdentifier, identifier)
                 ?: throw CqlCompilerException(
-                    String.format(
-                        Locale.US,
-                        "Could not find type for model: %s and name: %s",
-                        modelIdentifier,
-                        identifier
-                    ),
+                    "Could not find type for model: $modelIdentifier and name: $identifier",
                     getTrackBack(ctx)
                 )
         val result =
@@ -521,16 +499,17 @@ class Cql2ElmVisitor(
         }
     }
 
-    fun internalVisitExpressionDefinition(ctx: ExpressionDefinitionContext): ExpressionDef? {
+    private fun internalVisitExpressionDefinition(
+        ctx: ExpressionDefinitionContext
+    ): ExpressionDef? {
         val identifier = parseString(ctx.identifier())!!
         var def = libraryBuilder.resolveExpressionRef(identifier)
 
         // First time visiting this expression definition, create a lightweight ExpressionDef to be
-        // used to output a
-        // hiding warning message
-        // If it's the second time around, we'll be able to resolve it and we can assume it's
-        // already on the
-        // hiding stack.
+        // used to output a hiding warning message
+        //
+        // If it's the second time around, we'll be able to resolve it,
+        // and we can assume it's already on the hiding stack.
         if (def == null) {
             val hollowExpressionDef =
                 of.createExpressionDef().withName(identifier).withContext(currentContext)
@@ -540,7 +519,6 @@ class Cql2ElmVisitor(
             if (def != null && isImplicitContextExpressionDef(def)) {
                 libraryBuilder.removeExpression(def)
                 removeImplicitContextExpressionDef(def)
-                def = null
             }
             libraryBuilder.pushExpressionContext(currentContext)
             try {
@@ -571,15 +549,9 @@ class Cql2ElmVisitor(
         return try {
             val expressionDef = internalVisitExpressionDefinition(ctx)
             if (forwards.isEmpty() || forwards.peek().name != expressionDef!!.name) {
-                if (definedExpressionDefinitions.contains(expressionDef!!.name)) {
+                require(!definedExpressionDefinitions.contains(expressionDef!!.name)) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Identifier %s is already in use in this library.",
-                            expressionDef.name
-                        )
-                    )
+                    "Identifier ${expressionDef.name} is already in use in this library."
                 }
 
                 // Track defined expression definitions locally, otherwise duplicate expression
@@ -619,7 +591,7 @@ class Cql2ElmVisitor(
         )
     }
 
-    override fun visitTupleElementSelector(ctx: TupleElementSelectorContext): Any? {
+    override fun visitTupleElementSelector(ctx: TupleElementSelectorContext): TupleElement {
         val result =
             of.createTupleElement()
                 .withName(parseString(ctx.referentialIdentifier()))
@@ -627,7 +599,7 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitTupleSelector(ctx: TupleSelectorContext): Any? {
+    override fun visitTupleSelector(ctx: TupleSelectorContext): Tuple {
         val tuple = of.createTuple()
         val elements = mutableListOf<TupleTypeElement>()
         for (elementContext in ctx.tupleElementSelector()) {
@@ -639,14 +611,16 @@ class Cql2ElmVisitor(
         return tuple
     }
 
-    override fun visitInstanceElementSelector(ctx: InstanceElementSelectorContext): Any? {
+    override fun visitInstanceElementSelector(
+        ctx: InstanceElementSelectorContext
+    ): InstanceElement {
         val name = parseString(ctx.referentialIdentifier())
         val exp = parseExpression(ctx.expression())
         val result = of.createInstanceElement().withName(name).withValue(exp)
         return result
     }
 
-    override fun visitInstanceSelector(ctx: InstanceSelectorContext): Any {
+    override fun visitInstanceSelector(ctx: InstanceSelectorContext): Instance {
         val instance: Instance = of.createInstance()
         val classTypeSpecifier = visitNamedTypeSpecifier(ctx.namedTypeSpecifier())!!
         instance.classType = classTypeSpecifier.name
@@ -665,7 +639,7 @@ class Cql2ElmVisitor(
         return instance
     }
 
-    override fun visitCodeSelector(ctx: CodeSelectorContext): Any? {
+    override fun visitCodeSelector(ctx: CodeSelectorContext): Code {
         val code = of.createCode()
         code.code = parseString(ctx.STRING())
         code.system = visit(ctx.codesystemIdentifier()) as CodeSystemRef?
@@ -676,7 +650,7 @@ class Cql2ElmVisitor(
         return code
     }
 
-    override fun visitConceptSelector(ctx: ConceptSelectorContext): Any? {
+    override fun visitConceptSelector(ctx: ConceptSelectorContext): Concept {
         val concept = of.createConcept()
         if (ctx.displayClause() != null) {
             concept.display = parseString(ctx.displayClause()!!.STRING())
@@ -688,7 +662,7 @@ class Cql2ElmVisitor(
         return concept
     }
 
-    override fun visitListSelector(ctx: ListSelectorContext): Any? {
+    override fun visitListSelector(ctx: ListSelectorContext): org.hl7.elm.r1.List {
         val elementTypeSpecifier = parseTypeSpecifier(ctx.typeSpecifier())
         val list = of.createList()
         var listType: ListType? = null
@@ -743,7 +717,12 @@ class Cql2ElmVisitor(
         for (element in elements) {
             if (!elementType!!.isSuperTypeOf(element.resultType!!)) {
                 val conversion =
-                    libraryBuilder.findConversion(element.resultType!!, elementType, true, false)
+                    libraryBuilder.findConversion(
+                        element.resultType!!,
+                        elementType,
+                        implicit = true,
+                        allowPromotionAndDemotion = false
+                    )
                 if (conversion != null) {
                     list.element.add(libraryBuilder.convertExpression(element, conversion))
                 } else {
@@ -760,7 +739,7 @@ class Cql2ElmVisitor(
         return list
     }
 
-    override fun visitTimeLiteral(ctx: TimeLiteralContext): Any? {
+    override fun visitTimeLiteral(ctx: TimeLiteralContext): Time {
         var input = ctx.text
         if (input.startsWith("@")) {
             input = input.substring(1)
@@ -775,40 +754,26 @@ class Cql2ElmVisitor(
                 var minute = -1
                 var second = -1
                 var millisecond = -1
-                if (hour < 0 || hour > 24) {
-                    throw IllegalArgumentException(
-                        String.format(Locale.US, "Invalid hour in time literal (%s).", input)
-                    )
-                }
+                require(hour in 0..24) { "Invalid hour in time literal ($hour)." }
                 result.hour = libraryBuilder.createLiteral(hour)
                 if (matcher.group(3) != null) {
                     minute = matcher.group(3).toInt()
-                    if ((minute < 0) || (minute >= 60) || (hour == 24 && minute > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(Locale.US, "Invalid minute in time literal (%s).", input)
-                        )
+                    require(!((minute < 0) || (minute >= 60) || (hour == 24 && minute > 0))) {
+                        "Invalid minute in time literal ($minute)."
                     }
                     result.minute = libraryBuilder.createLiteral(minute)
                 }
                 if (matcher.group(5) != null) {
                     second = matcher.group(5).toInt()
-                    if ((second < 0) || (second >= 60) || (hour == 24 && second > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(Locale.US, "Invalid second in time literal (%s).", input)
-                        )
+                    require(!((second < 0) || (second >= 60) || (hour == 24 && second > 0))) {
+                        "Invalid second in time literal ($second)."
                     }
                     result.second = libraryBuilder.createLiteral(second)
                 }
                 if (matcher.group(7) != null) {
                     millisecond = matcher.group(7).toInt()
-                    if (millisecond < 0 || (hour == 24 && millisecond > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid millisecond in time literal (%s).",
-                                input
-                            )
-                        )
+                    require(hour == 24 && millisecond == 0 || millisecond >= 0) {
+                        "Invalid millisecond in time literal ($millisecond)."
                     }
                     result.millisecond = libraryBuilder.createLiteral(millisecond)
                 }
@@ -816,21 +781,14 @@ class Cql2ElmVisitor(
                 result
             } catch (e: RuntimeException) {
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Invalid time input (%s). Use ISO 8601 time representation (hh:mm:ss.fff).",
-                        input
-                    ),
+                    "Invalid time input ($input). Use ISO 8601 time representation (hh:mm:ss.fff).",
                     e
                 )
             }
         } else {
+            @Suppress("UseRequire")
             throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Invalid time input (%s). Use ISO 8601 time representation (hh:mm:ss.fff).",
-                    input
-                )
+                "Invalid time input ($input). Use ISO 8601 time representation (hh:mm:ss.fff)."
             )
         }
     }
@@ -905,15 +863,7 @@ class Cql2ElmVisitor(
                 result.year = libraryBuilder.createLiteral(year)
                 if (matcher.group(5) != null) {
                     month = matcher.group(5).toInt()
-                    if (month < 0 || month > 12) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid month in date/time literal (%s).",
-                                input
-                            )
-                        )
-                    }
+                    require(month in 0..12) { "Invalid month in date/time literal ($input)." }
                     result.month = libraryBuilder.createLiteral(month)
                 }
                 if (matcher.group(9) != null) {
@@ -925,68 +875,33 @@ class Cql2ElmVisitor(
                         6,
                         9,
                         11 -> maxDay = 30
-                        else -> {}
-                    }
-                    if (day < 0 || day > maxDay) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid day in date/time literal (%s).",
-                                input
-                            )
-                        )
                     }
+                    require(day in 0..maxDay) { "Invalid day in date/time literal ($input)." }
                     result.day = libraryBuilder.createLiteral(day)
                 }
                 if (matcher.group(13) != null) {
                     hour = matcher.group(13).toInt()
-                    if (hour < 0 || hour > 24) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid hour in date/time literal (%s).",
-                                input
-                            )
-                        )
-                    }
+                    require(hour in 0..24) { "Invalid hour in date/time literal ($input)." }
                     result.hour = libraryBuilder.createLiteral(hour)
                 }
                 if (matcher.group(15) != null) {
                     minute = matcher.group(15).toInt()
-                    if ((minute < 0) || (minute >= 60) || (hour == 24 && minute > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid minute in date/time literal (%s).",
-                                input
-                            )
-                        )
+                    require(minute in 0..60 && !(hour == 24 && minute > 0)) {
+                        "Invalid minute in date/time literal ($input)."
                     }
                     result.minute = libraryBuilder.createLiteral(minute)
                 }
                 if (matcher.group(17) != null) {
                     second = matcher.group(17).toInt()
-                    if ((second < 0) || (second >= 60) || (hour == 24 && second > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid second in date/time literal (%s).",
-                                input
-                            )
-                        )
+                    require(second in 0..60 && !(hour == 24 && second > 0)) {
+                        "Invalid second in date/time literal ($input)."
                     }
                     result.second = libraryBuilder.createLiteral(second)
                 }
                 if (matcher.group(19) != null) {
                     millisecond = matcher.group(19).toInt()
-                    if (millisecond < 0 || (hour == 24 && millisecond > 0)) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid millisecond in date/time literal (%s).",
-                                input
-                            )
-                        )
+                    require(millisecond >= 0 && !(hour == 24 && millisecond > 0)) {
+                        "Invalid millisecond in date/time literal ($input)."
                     }
                     result.millisecond = libraryBuilder.createLiteral(millisecond)
                 }
@@ -997,28 +912,12 @@ class Cql2ElmVisitor(
                     val offsetPolarity = if ((matcher.group(25) == "+")) 1 else -1
                     if (matcher.group(28) != null) {
                         val hourOffset = matcher.group(26).toInt()
-                        if (hourOffset < 0 || hourOffset > 14) {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Timezone hour offset is out of range in date/time literal (%s).",
-                                    input
-                                )
-                            )
+                        require(hourOffset in 0..14) {
+                            "Timezone hour offset is out of range in date/time literal ($input)."
                         }
                         val minuteOffset = matcher.group(28).toInt()
-                        if (
-                            (minuteOffset < 0) ||
-                                (minuteOffset >= 60) ||
-                                (hourOffset == 14 && minuteOffset > 0)
-                        ) {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Timezone minute offset is out of range in date/time literal (%s).",
-                                    input
-                                )
-                            )
+                        require(minuteOffset in 0..60 && !(hourOffset == 14 && minuteOffset > 0)) {
+                            "Timezone minute offset is out of range in date/time literal ($input)."
                         }
                         result.timezoneOffset =
                             libraryBuilder.createLiteral(
@@ -1027,14 +926,8 @@ class Cql2ElmVisitor(
                     } else {
                         if (matcher.group(26) != null) {
                             val hourOffset = matcher.group(26).toInt()
-                            if (hourOffset < 0 || hourOffset > 14) {
-                                throw IllegalArgumentException(
-                                    String.format(
-                                        Locale.US,
-                                        "Timezone hour offset is out of range in date/time literal (%s).",
-                                        input
-                                    )
-                                )
+                            require(hourOffset in 0..14) {
+                                "Timezone hour offset is out of range in date/time literal ($input)."
                             }
                             result.timezoneOffset =
                                 libraryBuilder.createLiteral(
@@ -1060,23 +953,16 @@ class Cql2ElmVisitor(
                 result
             } catch (e: RuntimeException) {
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Invalid date-time input (%s). Use ISO 8601 date time representation (yyyy-MM-ddThh:mm:ss.fff(Z|(+/-hh:mm)).",
-                        input
-                    ),
+                    "Invalid date-time input ($input)." +
+                        " Use ISO 8601 date time representation (yyyy-MM-ddThh:mm:ss.fff(Z|(+/-hh:mm)).",
                     e
                 )
             }
-        } else {
+        } else
             throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Invalid date-time input (%s). Use ISO 8601 date time representation (yyyy-MM-ddThh:mm:ss.fff(Z|+/-hh:mm)).",
-                    input
-                )
+                "Invalid date-time input ($input)." +
+                    " Use ISO 8601 date time representation (yyyy-MM-ddThh:mm:ss.fff(Z|+/-hh:mm))."
             )
-        }
     }
 
     override fun visitDateLiteral(ctx: DateLiteralContext): Any {
@@ -1095,7 +981,7 @@ class Cql2ElmVisitor(
         return parseDateTimeLiteral(input)
     }
 
-    override fun visitNullLiteral(ctx: NullLiteralContext): Null? {
+    override fun visitNullLiteral(ctx: NullLiteralContext): Null {
         val result = of.createNull()
         result.resultType = libraryBuilder.resolveTypeName("System", "Any")
         return result
@@ -1121,9 +1007,7 @@ class Cql2ElmVisitor(
         return try {
             BigDecimal(value)
         } catch (@Suppress("SwallowedException") e: Exception) {
-            throw IllegalArgumentException(
-                String.format(Locale.US, "Could not parse number literal: %s", value)
-            )
+            throw IllegalArgumentException("Could not parse number literal: $value")
         }
     }
 
@@ -1147,19 +1031,19 @@ class Cql2ElmVisitor(
         throw IllegalArgumentException("Could not create quantity from source expression.")
     }
 
-    override fun visitRatio(ctx: RatioContext): Expression {
+    override fun visitRatio(ctx: RatioContext): Ratio {
         val numerator = getQuantity(visit(ctx.quantity(0)!!) as Expression?)
         val denominator = getQuantity(visit(ctx.quantity(1)!!) as Expression?)
         return libraryBuilder.createRatio(numerator, denominator)
     }
 
-    override fun visitNotExpression(ctx: NotExpressionContext): Not? {
+    override fun visitNotExpression(ctx: NotExpressionContext): Not {
         val result = of.createNot().withOperand(parseExpression(ctx.expression()))
         libraryBuilder.resolveUnaryCall("System", "Not", result)
         return result
     }
 
-    override fun visitExistenceExpression(ctx: ExistenceExpressionContext): Exists? {
+    override fun visitExistenceExpression(ctx: ExistenceExpressionContext): Exists {
         val result = of.createExists().withOperand(parseExpression(ctx.expression()))
         libraryBuilder.resolveUnaryCall("System", "Exists", result)
         return result
@@ -1188,9 +1072,7 @@ class Cql2ElmVisitor(
                 operatorName = "Modulo"
             }
             else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unsupported operator: %s.", ctx.getChild(1)!!.text)
-                )
+                throw IllegalArgumentException("Unsupported operator: ${ctx.getChild(1)!!.text}.")
         }
         exp.withOperand(
             parseExpression(ctx.expressionTerm(0))!!,
@@ -1200,7 +1082,7 @@ class Cql2ElmVisitor(
         return exp
     }
 
-    override fun visitPowerExpressionTerm(ctx: PowerExpressionTermContext): Power? {
+    override fun visitPowerExpressionTerm(ctx: PowerExpressionTermContext): Power {
         val power =
             of.createPower()
                 .withOperand(
@@ -1220,7 +1102,7 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitAdditionExpressionTerm(ctx: AdditionExpressionTermContext): Expression? {
+    override fun visitAdditionExpressionTerm(ctx: AdditionExpressionTermContext): Expression {
         var exp: Expression?
         val operatorName: String?
         when (ctx.getChild(1)!!.text) {
@@ -1237,9 +1119,7 @@ class Cql2ElmVisitor(
                 operatorName = "Concatenate"
             }
             else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unsupported operator: %s.", ctx.getChild(1)!!.text)
-                )
+                throw IllegalArgumentException("Unsupported operator: ${ctx.getChild(1)!!.text}.")
         }
         if (exp is BinaryExpression) {
             exp.withOperand(
@@ -1254,7 +1134,7 @@ class Cql2ElmVisitor(
                 exp = concatenate
             }
         } else {
-            val concatenate: Concatenate? = exp as Concatenate?
+            val concatenate = exp as Concatenate?
             concatenate!!.withOperand(
                 parseExpression(ctx.expressionTerm(0))!!,
                 parseExpression(ctx.expressionTerm(1))!!
@@ -1283,13 +1163,15 @@ class Cql2ElmVisitor(
 
     override fun visitElementExtractorExpressionTerm(
         ctx: ElementExtractorExpressionTermContext
-    ): Any? {
+    ): SingletonFrom {
         val result = of.createSingletonFrom().withOperand(parseExpression(ctx.expressionTerm()))
         libraryBuilder.resolveUnaryCall("System", "SingletonFrom", result)
         return result
     }
 
-    override fun visitPointExtractorExpressionTerm(ctx: PointExtractorExpressionTermContext): Any? {
+    override fun visitPointExtractorExpressionTerm(
+        ctx: PointExtractorExpressionTermContext
+    ): PointFrom {
         val result = of.createPointFrom().withOperand(parseExpression(ctx.expressionTerm()))
         libraryBuilder.resolveUnaryCall("System", "PointFrom", result)
         return result
@@ -1305,10 +1187,7 @@ class Cql2ElmVisitor(
             "maximum" -> {
                 libraryBuilder.buildMaximum(targetType!!.resultType)
             }
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown extent: %s", extent)
-                )
+            else -> throw IllegalArgumentException("Unknown extent: $extent")
         }
     }
 
@@ -1327,7 +1206,11 @@ class Cql2ElmVisitor(
     }
 
     private fun parseComparableDateTimePrecision(dateTimePrecision: String): DateTimePrecision? {
-        return parseDateTimePrecision(dateTimePrecision, true, false)
+        return parseDateTimePrecision(
+            dateTimePrecision,
+            precisionRequired = true,
+            allowWeeks = false
+        )
     }
 
     private fun parseComparableDateTimePrecision(
@@ -1374,10 +1257,7 @@ class Cql2ElmVisitor(
             "ms",
             "millisecond",
             "milliseconds" -> DateTimePrecision.MILLISECOND
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown precision '%s'.", dateTimePrecision)
-                )
+            else -> throw IllegalArgumentException("Unknown precision '$dateTimePrecision'.")
         }
     }
 
@@ -1421,16 +1301,13 @@ class Cql2ElmVisitor(
             }
             "week" ->
                 throw IllegalArgumentException("Date/time values do not have a week component.")
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown precision '%s'.", component)
-                )
+            else -> throw IllegalArgumentException("Unknown precision '$component'.")
         }
         libraryBuilder.resolveUnaryCall("System", operatorName, result)
         return result
     }
 
-    override fun visitDurationExpressionTerm(ctx: DurationExpressionTermContext): Any? {
+    override fun visitDurationExpressionTerm(ctx: DurationExpressionTermContext): DurationBetween {
         // duration in days of X <=> days between start of X and end of X
         val operand = parseExpression(ctx.expressionTerm())
         val start = of.createStart().withOperand(operand)
@@ -1445,7 +1322,9 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitDifferenceExpressionTerm(ctx: DifferenceExpressionTermContext): Any? {
+    override fun visitDifferenceExpressionTerm(
+        ctx: DifferenceExpressionTermContext
+    ): DifferenceBetween {
         // difference in days of X <=> difference in days between start of X and end of
         // X
         val operand = parseExpression(ctx.expressionTerm())
@@ -1461,7 +1340,7 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitBetweenExpression(ctx: BetweenExpressionContext): Any? {
+    override fun visitBetweenExpression(ctx: BetweenExpressionContext): Expression {
         // X properly? between Y and Z
         val first = parseExpression(ctx.expression())!!
         val second = parseExpression(ctx.expressionTerm(0))!!
@@ -1615,10 +1494,10 @@ class Cql2ElmVisitor(
                     return contains
                 }
         }
-        throw IllegalArgumentException(String.format(Locale.US, "Unknown operator: %s", operator))
+        throw IllegalArgumentException("Unknown operator: $operator")
     }
 
-    override fun visitAndExpression(ctx: AndExpressionContext): And? {
+    override fun visitAndExpression(ctx: AndExpressionContext): And {
         val and =
             of.createAnd()
                 .withOperand(
@@ -1629,7 +1508,7 @@ class Cql2ElmVisitor(
         return and
     }
 
-    override fun visitOrExpression(ctx: OrExpressionContext): Expression? {
+    override fun visitOrExpression(ctx: OrExpressionContext): Expression {
         return if (ctx.getChild(1)!!.text == "xor") {
             val xor =
                 of.createXor()
@@ -1651,7 +1530,7 @@ class Cql2ElmVisitor(
         }
     }
 
-    override fun visitImpliesExpression(ctx: ImpliesExpressionContext): Expression? {
+    override fun visitImpliesExpression(ctx: ImpliesExpressionContext): Implies {
         val implies =
             of.createImplies()
                 .withOperand(
@@ -1662,7 +1541,7 @@ class Cql2ElmVisitor(
         return implies
     }
 
-    override fun visitInFixSetExpression(ctx: InFixSetExpressionContext): Any? {
+    override fun visitInFixSetExpression(ctx: InFixSetExpressionContext): Expression {
         val operator = ctx.getChild(1)!!.text
         val left = parseExpression(ctx.expression(0))
         val right = parseExpression(ctx.expression(1))
@@ -1675,10 +1554,10 @@ class Cql2ElmVisitor(
         return of.createNull()
     }
 
-    override fun visitEqualityExpression(ctx: EqualityExpressionContext): Expression? {
+    override fun visitEqualityExpression(ctx: EqualityExpressionContext): Expression {
         val operator = parseString(ctx.getChild(1))
         return if (operator == "~" || operator == "!~") {
-            val equivalent: BinaryExpression =
+            val equivalent =
                 of.createEquivalent()
                     .withOperand(
                         parseExpression(ctx.expression(0))!!,
@@ -1693,7 +1572,7 @@ class Cql2ElmVisitor(
             }
             equivalent
         } else {
-            val equal: BinaryExpression =
+            val equal =
                 of.createEqual()
                     .withOperand(
                         parseExpression(ctx.expression(0))!!,
@@ -1730,10 +1609,7 @@ class Cql2ElmVisitor(
                 operatorName = "GreaterOrEqual"
                 exp = of.createGreaterOrEqual()
             }
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown operator: %s", ctx.getChild(1)!!.text)
-                )
+            else -> throw IllegalArgumentException("Unknown operator: ${ctx.getChild(1)!!.text}")
         }
         exp.withOperand(parseExpression(ctx.expression(0))!!, parseExpression(ctx.expression(1))!!)
         libraryBuilder.resolveBinaryCall("System", operatorName, exp)
@@ -1786,15 +1662,8 @@ class Cql2ElmVisitor(
 
     override fun visitTermExpression(ctx: TermExpressionContext): Any? {
         val result = super.visitTermExpression(ctx)
-        if (result is LibraryRef) {
-            // ERROR:
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Identifier %s is a library and cannot be used as an expression.",
-                    result.libraryName
-                )
-            )
+        require(result !is LibraryRef) {
+            "Identifier ${(result as LibraryRef).libraryName} is a library and cannot be used as an expression."
         }
         return result
     }
@@ -1835,17 +1704,12 @@ class Cql2ElmVisitor(
                     libraryBuilder.findConversion(
                         operand.resultType!!,
                         targetType.resultType!!,
-                        false,
-                        true
+                        implicit = false,
+                        allowPromotionAndDemotion = true
                     )
                         ?: // ERROR:
                         throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Could not resolve conversion from type %s to type %s.",
-                                operand.resultType,
-                                targetType.resultType
-                            )
+                            "Could not resolve conversion from type ${operand.resultType} to type ${targetType.resultType}."
                         )
                 return libraryBuilder.convertExpression((operand), conversion)
             }
@@ -1863,7 +1727,7 @@ class Cql2ElmVisitor(
         }
     }
 
-    override fun visitTypeExpression(ctx: TypeExpressionContext): Any? {
+    override fun visitTypeExpression(ctx: TypeExpressionContext): Expression {
         // NOTE: These don't use the buildIs or buildAs because those start with a
         // DataType, rather than a TypeSpecifier
         if (ctx.getChild(1)!!.text == "is") {
@@ -1885,7 +1749,7 @@ class Cql2ElmVisitor(
         return asExpression
     }
 
-    override fun visitCastExpression(ctx: CastExpressionContext): Any? {
+    override fun visitCastExpression(ctx: CastExpressionContext): As {
         // NOTE: This doesn't use buildAs because it starts with a DataType, rather than
         // a TypeSpecifier
         val asExpression =
@@ -1899,7 +1763,7 @@ class Cql2ElmVisitor(
         return asExpression
     }
 
-    override fun visitBooleanExpression(ctx: BooleanExpressionContext): Expression? {
+    override fun visitBooleanExpression(ctx: BooleanExpressionContext): Expression {
         var exp: UnaryExpression?
         val left = visit(ctx.expression()) as Expression?
         val lastChild = ctx.getChild(ctx.childCount - 1)!!.text
@@ -1917,16 +1781,14 @@ class Cql2ElmVisitor(
                 exp = of.createIsFalse().withOperand(left)
                 libraryBuilder.resolveUnaryCall("System", "IsFalse", exp)
             }
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown boolean test predicate %s.", lastChild)
-                )
+            else -> throw IllegalArgumentException("Unknown boolean test predicate $lastChild.")
         }
         if ("not" == nextToLast) {
             track(exp, ctx)
             exp = of.createNot().withOperand(exp)
             libraryBuilder.resolveUnaryCall("System", "Not", exp)
         }
+
         return exp
     }
 
@@ -1946,7 +1808,7 @@ class Cql2ElmVisitor(
 
     override fun visitConcurrentWithIntervalOperatorPhrase(
         ctx: ConcurrentWithIntervalOperatorPhraseContext
-    ): Any? {
+    ): BinaryExpression {
         // ('starts' | 'ends' | 'occurs')? 'same' dateTimePrecision? (relativeQualifier
         // | 'as') ('start' | 'end')?
         val timingOperator: TimingOperatorContext = timingOperators.peek()
@@ -2020,11 +1882,7 @@ class Cql2ElmVisitor(
                 }
                 else ->
                     throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Unknown relative qualifier: '%s'.",
-                            ctx.relativeQualifier()!!.text
-                        )
+                        "Unknown relative qualifier: '${ctx.relativeQualifier()!!.text}'."
                     )
             }
         }
@@ -2178,7 +2036,7 @@ class Cql2ElmVisitor(
 
     override fun visitBeforeOrAfterIntervalOperatorPhrase(
         ctx: BeforeOrAfterIntervalOperatorPhraseContext
-    ): Any? {
+    ): Expression {
         // ('starts' | 'ends' | 'occurs')? quantityOffset? ('before' | 'after')
         // dateTimePrecisionSpecifier? ('start' |
         // 'end')?
@@ -2268,8 +2126,8 @@ class Cql2ElmVisitor(
                         "System",
                         "SameOrBefore",
                         sameOrBefore,
-                        true,
-                        true
+                        mustResolve = true,
+                        allowPromotionAndDemotion = true
                     )
                     sameOrBefore
                 } else {
@@ -2283,8 +2141,8 @@ class Cql2ElmVisitor(
                         "System",
                         "SameOrAfter",
                         sameOrAfter,
-                        true,
-                        true
+                        mustResolve = true,
+                        allowPromotionAndDemotion = true
                     )
                     sameOrAfter
                 }
@@ -2295,7 +2153,13 @@ class Cql2ElmVisitor(
                     if (dateTimePrecision != null) {
                         before.precision = parseComparableDateTimePrecision(dateTimePrecision)
                     }
-                    libraryBuilder.resolveBinaryCall("System", "Before", before, true, true)
+                    libraryBuilder.resolveBinaryCall(
+                        "System",
+                        "Before",
+                        before,
+                        mustResolve = true,
+                        allowPromotionAndDemotion = true
+                    )
                     before
                 } else {
                     val after =
@@ -2303,7 +2167,13 @@ class Cql2ElmVisitor(
                     if (dateTimePrecision != null) {
                         after.precision = parseComparableDateTimePrecision(dateTimePrecision)
                     }
-                    libraryBuilder.resolveBinaryCall("System", "After", after, true, true)
+                    libraryBuilder.resolveBinaryCall(
+                        "System",
+                        "After",
+                        after,
+                        mustResolve = true,
+                        allowPromotionAndDemotion = true
+                    )
                     after
                 }
             }
@@ -2390,8 +2260,8 @@ class Cql2ElmVisitor(
                                     "System",
                                     "Before",
                                     before,
-                                    true,
-                                    true
+                                    mustResolve = true,
+                                    allowPromotionAndDemotion = true
                                 )
                                 before
                             } else {
@@ -2406,8 +2276,8 @@ class Cql2ElmVisitor(
                                     "System",
                                     "SameOrBefore",
                                     sameOrBefore,
-                                    true,
-                                    true
+                                    mustResolve = true,
+                                    allowPromotionAndDemotion = true
                                 )
                                 sameOrBefore
                             }
@@ -2428,8 +2298,8 @@ class Cql2ElmVisitor(
                                     "System",
                                     "After",
                                     after,
-                                    true,
-                                    true
+                                    mustResolve = true,
+                                    allowPromotionAndDemotion = true
                                 )
                                 after
                             } else {
@@ -2444,8 +2314,8 @@ class Cql2ElmVisitor(
                                     "System",
                                     "SameOrAfter",
                                     sameOrAfter,
-                                    true,
-                                    true
+                                    mustResolve = true,
+                                    allowPromotionAndDemotion = true
                                 )
                                 sameOrAfter
                             }
@@ -2532,24 +2402,9 @@ class Cql2ElmVisitor(
         throw IllegalArgumentException("Unable to resolve interval operator phrase.")
     }
 
-    @Suppress("UnusedPrivateMember")
-    private fun resolveBetweenOperator(
-        unit: String?,
-        left: Expression,
-        right: Expression
-    ): BinaryExpression? {
-        if (unit != null) {
-            val between =
-                of.createDurationBetween()
-                    .withPrecision(parseDateTimePrecision(unit))
-                    .withOperand(left, right)
-            libraryBuilder.resolveBinaryCall("System", "DurationBetween", between)
-            return between
-        }
-        return null
-    }
-
-    override fun visitWithinIntervalOperatorPhrase(ctx: WithinIntervalOperatorPhraseContext): Any? {
+    override fun visitWithinIntervalOperatorPhrase(
+        ctx: WithinIntervalOperatorPhraseContext
+    ): Expression {
         // ('starts' | 'ends' | 'occurs')? 'properly'? 'within' quantityLiteral 'of'
         // ('start' | 'end')?
         // A starts within 3 days of start B
@@ -2714,7 +2569,9 @@ class Cql2ElmVisitor(
         return operator
     }
 
-    override fun visitStartsIntervalOperatorPhrase(ctx: StartsIntervalOperatorPhraseContext): Any? {
+    override fun visitStartsIntervalOperatorPhrase(
+        ctx: StartsIntervalOperatorPhraseContext
+    ): Starts {
         val dateTimePrecision =
             if (ctx.dateTimePrecisionSpecifier() != null)
                 ctx.dateTimePrecisionSpecifier()!!.dateTimePrecision().text
@@ -2729,7 +2586,7 @@ class Cql2ElmVisitor(
         return starts
     }
 
-    override fun visitEndsIntervalOperatorPhrase(ctx: EndsIntervalOperatorPhraseContext): Any? {
+    override fun visitEndsIntervalOperatorPhrase(ctx: EndsIntervalOperatorPhraseContext): Ends {
         val dateTimePrecision =
             if (ctx.dateTimePrecisionSpecifier() != null)
                 ctx.dateTimePrecisionSpecifier()!!.dateTimePrecision().text
@@ -2831,13 +2688,13 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitCaseExpressionItem(ctx: CaseExpressionItemContext): Any? {
+    override fun visitCaseExpressionItem(ctx: CaseExpressionItemContext): CaseItem {
         return of.createCaseItem()
             .withWhen(parseExpression(ctx.expression(0)))
             .withThen(parseExpression(ctx.expression(1)))
     }
 
-    override fun visitAggregateExpressionTerm(ctx: AggregateExpressionTermContext): Any? {
+    override fun visitAggregateExpressionTerm(ctx: AggregateExpressionTermContext): Expression {
         when (ctx.getChild(0)!!.text) {
             "distinct" -> {
                 val distinct = of.createDistinct().withOperand(parseExpression(ctx.expression()))
@@ -2850,9 +2707,7 @@ class Cql2ElmVisitor(
                 return flatten
             }
         }
-        throw IllegalArgumentException(
-            String.format(Locale.US, "Unknown aggregate operator %s.", ctx.getChild(0)!!.text)
-        )
+        throw IllegalArgumentException("Unknown aggregate operator ${ctx.getChild(0)!!.text}.")
     }
 
     override fun visitSetAggregateExpressionTerm(ctx: SetAggregateExpressionTermContext): Any {
@@ -2906,9 +2761,7 @@ class Cql2ElmVisitor(
                 return collapse
             }
         }
-        throw IllegalArgumentException(
-            String.format(Locale.US, "Unknown aggregate set operator %s.", ctx.getChild(0)!!.text)
-        )
+        throw IllegalArgumentException("Unknown aggregate set operator ${ctx.getChild(0)!!.text}.")
     }
 
     override fun visitRetrieve(ctx: RetrieveContext): Expression? {
@@ -2920,22 +2773,13 @@ class Cql2ElmVisitor(
                 qualifiers,
                 (parseString(ctx.namedTypeSpecifier().referentialOrTypeNameIdentifier()))!!
             )
-        val dataType: DataType =
-            libraryBuilder.resolveTypeName(model, label)
-                ?: // ERROR:
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Could not resolve type name %s.", label)
-                )
-        if (dataType !is ClassType || !dataType.isRetrievable) {
-            // ERROR:
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Specified data type %s does not support retrieval.",
-                    label
-                )
-            )
+        val dataType = libraryBuilder.resolveTypeName(model, label)
+
+        requireNotNull(dataType) { "Could not resolve type name $label." }
+        require(dataType is ClassType && dataType.isRetrievable) {
+            "Specified data type $label does not support retrieval."
         }
+
         val classType: ClassType = dataType
         // BTR -> The original intent of this code was to have the retrieve return the
         // base type, and use the
@@ -2992,12 +2836,7 @@ class Cql2ElmVisitor(
                     // WARNING:
                     propertyException =
                         CqlSemanticException(
-                            String.format(
-                                Locale.US,
-                                "Could not resolve code path %s for the type of the retrieve %s.",
-                                codePath,
-                                namedType.name
-                            ),
+                            "Could not resolve code path $codePath for the type of the retrieve ${namedType.name}.",
                             if (useStrictRetrieveTyping) CqlCompilerException.ErrorSeverity.Error
                             else CqlCompilerException.ErrorSeverity.Warning,
                             getTrackBack(ctx),
@@ -3007,7 +2846,7 @@ class Cql2ElmVisitor(
                 }
             }
             if (ctx.terminology()!!.qualifiedIdentifierExpression() != null) {
-                val identifiers = visit(ctx.terminology()!!) as List<String>
+                val identifiers: List<String> = visit(ctx.terminology()!!).cast()
                 terminology = resolveQualifiedIdentifier(identifiers)
                 track(terminology, ctx.terminology()!!.qualifiedIdentifierExpression()!!)
             } else {
@@ -3027,10 +2866,10 @@ class Cql2ElmVisitor(
                     (hasFHIRHelpers &&
                         propertyType is NamedType &&
                         ((propertyType as NamedType).simpleName == "Reference") &&
-                        ((namedType.simpleName == "MedicationRequest" ||
+                        (namedType.simpleName == "MedicationRequest" ||
                             namedType.simpleName == "MedicationAdministration" ||
                             namedType.simpleName == "MedicationDispense" ||
-                            namedType.simpleName == "MedicationStatement")))
+                            namedType.simpleName == "MedicationStatement"))
                 ) {
                     // TODO: This is a model-specific special case to support QICore
                     // This functionality needs to be generalized to a retrieve mapping in the model
@@ -3105,14 +2944,10 @@ class Cql2ElmVisitor(
                     libraryBuilder.resolveBinaryCall("System", "Equal", e)
 
                     // Apply target mapping if this is a profile-informed model info
-                    if (
-                        DataTypes.equal(idType, libraryBuilder.resolveTypeName("System", "String"))
-                    ) {
+                    if (equal(idType, libraryBuilder.resolveTypeName("System", "String"))) {
                         idProperty.path = "id.value"
                     }
-                    if (
-                        DataTypes.equal(refType, libraryBuilder.resolveTypeName("System", "String"))
-                    ) {
+                    if (equal(refType, libraryBuilder.resolveTypeName("System", "String"))) {
                         refProperty.path = "medication.reference.value"
                     }
                     val mCodeType: DataType? =
@@ -3237,7 +3072,7 @@ class Cql2ElmVisitor(
                 .withTemplateId(classType.identifier)
                 .withCodeProperty(codePath)
         if (ctx.contextIdentifier() != null) {
-            val identifiers = visit(ctx.contextIdentifier()!!) as List<String>
+            val identifiers: List<String> = visit(ctx.contextIdentifier()!!).cast()
             val contextExpression: Expression? = resolveQualifiedIdentifier(identifiers)
             retrieve.context = contextExpression
         }
@@ -3303,11 +3138,7 @@ class Cql2ElmVisitor(
                                 // WARNING:
                                 libraryBuilder.recordParsingException(
                                     CqlSemanticException(
-                                        String.format(
-                                            Locale.US,
-                                            "Unexpected membership operator %s in retrieve",
-                                            inExpression.javaClass.simpleName
-                                        ),
+                                        "Unexpected membership operator ${inExpression.javaClass.simpleName} in retrieve",
                                         if (useStrictRetrieveTyping)
                                             CqlCompilerException.ErrorSeverity.Error
                                         else CqlCompilerException.ErrorSeverity.Warning,
@@ -3347,13 +3178,13 @@ class Cql2ElmVisitor(
 
                         // Automatically promote to a list for use in the retrieve target
                         if (
-                            !((equivalent.operand[1].resultType is ListType ||
+                            !(equivalent.operand[1].resultType is ListType ||
                                 (libraryBuilder.isCompatibleWith("1.5") &&
                                     equivalent.operand[1]
                                         .resultType!!
                                         .isSubTypeOf(
                                             libraryBuilder.resolveTypeName("System", "Vocabulary")!!
-                                        ))))
+                                        )))
                         ) {
                             retrieve.codes = libraryBuilder.resolveToList(equivalent.operand[1])
                         } else {
@@ -3369,13 +3200,13 @@ class Cql2ElmVisitor(
 
                         // Automatically promote to a list for use in the retrieve target
                         if (
-                            !((equal.operand[1].resultType is ListType ||
+                            !(equal.operand[1].resultType is ListType ||
                                 (libraryBuilder.isCompatibleWith("1.5") &&
                                     equal.operand[1]
                                         .resultType!!
                                         .isSubTypeOf(
                                             libraryBuilder.resolveTypeName("System", "Vocabulary")!!
-                                        ))))
+                                        )))
                         ) {
                             retrieve.codes = libraryBuilder.resolveToList(equal.operand[1])
                         } else {
@@ -3386,11 +3217,7 @@ class Cql2ElmVisitor(
                         // WARNING:
                         libraryBuilder.recordParsingException(
                             CqlSemanticException(
-                                String.format(
-                                    Locale.US,
-                                    "Unknown code comparator %s in retrieve",
-                                    codeComparator
-                                ),
+                                "Unknown code comparator $codeComparator in retrieve",
                                 if (useStrictRetrieveTyping)
                                     CqlCompilerException.ErrorSeverity.Error
                                 else CqlCompilerException.ErrorSeverity.Warning,
@@ -3485,7 +3312,7 @@ class Cql2ElmVisitor(
         }
         val sources: MutableList<AliasedQuerySource?> = ArrayList()
         for (source in ctx.aliasedQuerySource()) {
-            require(!(sources.size > 0 && !hasFrom)) {
+            require(!(sources.isNotEmpty() && !hasFrom)) {
                 "The from keyword is required for multi-source queries."
             }
             sources.add(visit(source) as AliasedQuerySource?)
@@ -3493,14 +3320,14 @@ class Cql2ElmVisitor(
         return sources
     }
 
-    override fun visitQuery(ctx: cqlParser.QueryContext): Any? {
+    override fun visitQuery(ctx: cqlParser.QueryContext): Query {
         val queryContext = QueryContext()
         libraryBuilder.pushQueryContext(queryContext)
         var sources: List<AliasedQuerySource>? = null
         return try {
             queryContext.enterSourceClause()
             try {
-                sources = visit(ctx.sourceClause()) as List<AliasedQuerySource>?
+                sources = visit(ctx.sourceClause()).cast()
             } finally {
                 queryContext.exitSourceClause()
             }
@@ -3526,9 +3353,7 @@ class Cql2ElmVisitor(
              */
             var dfcx: List<LetClause> = emptyList()
             try {
-                dfcx =
-                    if (ctx.letClause() != null) visit(ctx.letClause()!!) as List<LetClause>
-                    else dfcx
+                dfcx = if (ctx.letClause() != null) visit(ctx.letClause()!!).cast() else dfcx
                 for (letClause: LetClause in dfcx) {
                     libraryBuilder.pushIdentifier(letClause.identifier!!, letClause)
                 }
@@ -3637,16 +3462,14 @@ class Cql2ElmVisitor(
                 if (expressionContextPushed) {
                     libraryBuilder.popExpressionContext()
                 }
-                if (dfcx != null) {
-                    for (letClause: LetClause? in dfcx) {
-                        libraryBuilder.popIdentifier()
-                    }
+                for (letClause in dfcx) {
+                    libraryBuilder.popIdentifier()
                 }
             }
         } finally {
             libraryBuilder.popQueryContext()
             if (sources != null) {
-                for (source: AliasedQuerySource? in sources) {
+                for (source in sources) {
                     libraryBuilder.popIdentifier()
                 }
             }
@@ -3724,17 +3547,17 @@ class Cql2ElmVisitor(
      * @return The collapsed path operands (or sub-operands) were modified; `false` otherwise.
      */
     private fun getPropertyPath(reference: Expression, alias: String): String? {
-        var reference = reference
-        reference = getConversionReference(reference)
-        reference = getChoiceSelection(reference)
-        if (reference is Property) {
-            val property = reference
+        var ref = reference
+        ref = getConversionReference(ref)
+        ref = getChoiceSelection(ref)
+        if (ref is Property) {
+            val property = ref
             if (alias == property.scope) {
                 return property.path
             } else if (property.source != null) {
                 val subPath = getPropertyPath(property.source!!, alias)
                 if (subPath != null) {
-                    return String.format(Locale.US, "%s.%s", subPath, property.path)
+                    return "$subPath.${property.path}"
                 }
             }
         }
@@ -3837,14 +3660,11 @@ class Cql2ElmVisitor(
         var result: Expression = and
         val lhs = and.operand[0]
         val rhs = and.operand[1]
-        if (isBooleanLiteral(lhs, true)) {
-            result = rhs
-        } else if (isBooleanLiteral(rhs, true)) {
-            result = lhs
-        } else if (lhs is And) {
-            and.operand[0] = consolidateAnd(lhs)
-        } else if (rhs is And) {
-            and.operand[1] = consolidateAnd(rhs)
+        when {
+            isBooleanLiteral(lhs, true) -> result = rhs
+            isBooleanLiteral(rhs, true) -> result = lhs
+            lhs is And -> and.operand[0] = consolidateAnd(lhs)
+            rhs is And -> and.operand[1] = consolidateAnd(rhs)
         }
         return result
     }
@@ -3912,11 +3732,6 @@ class Cql2ElmVisitor(
         // return isEligible;
     }
 
-    @Suppress("UnusedPrivateMember")
-    private fun isDateTimeTypeSpecifier(e: Element): Boolean {
-        return e.resultType == libraryBuilder.resolveTypeName("System", "DateTime")
-    }
-
     override fun visitLetClause(ctx: LetClauseContext): Any {
         val letClauseItems: MutableList<LetClause?> = ArrayList()
         for (letClauseItem in ctx.letClauseItem()) {
@@ -3925,7 +3740,7 @@ class Cql2ElmVisitor(
         return letClauseItems
     }
 
-    override fun visitLetClauseItem(ctx: LetClauseItemContext): Any? {
+    override fun visitLetClauseItem(ctx: LetClauseItemContext): LetClause {
         val letClause =
             of.createLetClause()
                 .withExpression(parseExpression(ctx.expression()))
@@ -3935,7 +3750,7 @@ class Cql2ElmVisitor(
         return letClause
     }
 
-    override fun visitAliasedQuerySource(ctx: AliasedQuerySourceContext): Any? {
+    override fun visitAliasedQuerySource(ctx: AliasedQuerySourceContext): AliasedQuerySource {
         val source =
             of.createAliasedQuerySource()
                 .withExpression(parseExpression(ctx.querySource()))
@@ -3980,13 +3795,12 @@ class Cql2ElmVisitor(
         return result
     }
 
-    override fun visitReturnClause(ctx: ReturnClauseContext): Any? {
+    override fun visitReturnClause(ctx: ReturnClauseContext): ReturnClause {
         val returnClause = of.createReturnClause()
         if (ctx.getChild(1) is TerminalNode) {
             when (ctx.getChild(1)!!.text) {
                 "all" -> returnClause.distinct = false
                 "distinct" -> returnClause.distinct = true
-                else -> {}
             }
         }
         returnClause.expression = parseExpression(ctx.expression())
@@ -4008,14 +3822,13 @@ class Cql2ElmVisitor(
         } else null
     }
 
-    override fun visitAggregateClause(ctx: AggregateClauseContext): Any? {
+    override fun visitAggregateClause(ctx: AggregateClauseContext): AggregateClause {
         libraryBuilder.checkCompatibilityLevel("Aggregate query clause", "1.5")
         val aggregateClause = of.createAggregateClause()
         if (ctx.getChild(1) is TerminalNode) {
             when (ctx.getChild(1)!!.text) {
                 "all" -> aggregateClause.distinct = false
                 "distinct" -> aggregateClause.distinct = true
-                else -> {}
             }
         }
         if (ctx.startingClause() != null) {
@@ -4047,11 +3860,11 @@ class Cql2ElmVisitor(
         return aggregateClause
     }
 
-    override fun visitSortDirection(ctx: SortDirectionContext): SortDirection? {
+    override fun visitSortDirection(ctx: SortDirectionContext): SortDirection {
         return SortDirection.fromValue(ctx.text)
     }
 
-    private fun parseSortDirection(ctx: SortDirectionContext?): SortDirection? {
+    private fun parseSortDirection(ctx: SortDirectionContext?): SortDirection {
         return if (ctx != null) {
             visitSortDirection(ctx)
         } else SortDirection.ASC
@@ -4063,15 +3876,15 @@ class Cql2ElmVisitor(
             of.createByColumn()
                 .withPath(sortExpression.name)
                 .withDirection(parseSortDirection(ctx.sortDirection()))
-                .withResultType(sortExpression.resultType) as SortByItem
+                .withResultType(sortExpression.resultType)
         } else
             of.createByExpression()
                 .withExpression(sortExpression)
                 .withDirection(parseSortDirection(ctx.sortDirection()))
-                .withResultType(sortExpression.resultType) as SortByItem
+                .withResultType(sortExpression.resultType)
     }
 
-    override fun visitSortClause(ctx: SortClauseContext): Any? {
+    override fun visitSortClause(ctx: SortClauseContext): SortClause {
         if (ctx.sortDirection() != null) {
             return of.createSortClause()
                 .withBy(
@@ -4091,12 +3904,12 @@ class Cql2ElmVisitor(
         } else if (ctx.retrieve() != null) {
             visit(ctx.retrieve()!!)
         } else {
-            val identifiers = visit(ctx.qualifiedIdentifierExpression()!!) as List<String>
+            val identifiers: List<String> = visit(ctx.qualifiedIdentifierExpression()!!).cast()
             resolveQualifiedIdentifier(identifiers)
         }
     }
 
-    override fun visitIndexedExpressionTerm(ctx: IndexedExpressionTermContext): Any? {
+    override fun visitIndexedExpressionTerm(ctx: IndexedExpressionTermContext): Indexer {
         val indexer =
             of.createIndexer()
                 .withOperand(
@@ -4139,7 +3952,7 @@ class Cql2ElmVisitor(
         return resolveMemberIdentifier(identifier)
     }
 
-    fun resolveQualifiedIdentifier(identifiers: List<String>): Expression? {
+    private fun resolveQualifiedIdentifier(identifiers: List<String>): Expression? {
         var current: Expression? = null
         for (identifier in identifiers) {
             current =
@@ -4152,7 +3965,7 @@ class Cql2ElmVisitor(
         return current
     }
 
-    fun resolveMemberIdentifier(identifier: String): Expression? {
+    private fun resolveMemberIdentifier(identifier: String): Expression? {
         if (libraryBuilder.hasExpressionTarget()) {
             val target = libraryBuilder.popExpressionTarget()
             return try {
@@ -4178,15 +3991,9 @@ class Cql2ElmVisitor(
                     chunks = Stack()
                     forwards.push(expressionInfo)
                     try {
-                        if (expressionInfo.definition == null) {
+                        requireNotNull(expressionInfo.definition) {
                             // ERROR:
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Could not validate reference to expression %s because its definition contains errors.",
-                                    expressionInfo.name
-                                )
-                            )
+                            "Could not validate reference to expression ${expressionInfo.name} because its definition contains errors."
                         }
 
                         // Have to call the visit to get the outer processing to occur
@@ -4209,19 +4016,19 @@ class Cql2ElmVisitor(
     }
 
     private fun ensureSystemFunctionName(libraryName: String?, functionName: String): String {
-        var functionName = functionName
         if (libraryName == null || libraryName == "System") {
             // Because these functions can be both a keyword and the name of a method, they
             // can be resolved by the
             // parser as a function, instead of as the keyword-based parser rule. In this
             // case, the function
             // name needs to be translated to the System function name in order to resolve.
-            when (functionName) {
-                "contains" -> functionName = "Contains"
-                "distinct" -> functionName = "Distinct"
-                "exists" -> functionName = "Exists"
-                "in" -> functionName = "In"
-                "not" -> functionName = "Not"
+            return when (functionName) {
+                "contains" -> "Contains"
+                "distinct" -> "Distinct"
+                "exists" -> "Exists"
+                "in" -> "In"
+                "not" -> "Not"
+                else -> functionName
             }
         }
         return functionName
@@ -4238,7 +4045,14 @@ class Cql2ElmVisitor(
                 expressions.add(visit(expressionContext) as Expression)
             }
         }
-        return resolveFunction(libraryName, functionName, expressions, true, false, false)
+        return resolveFunction(
+            libraryName,
+            functionName,
+            expressions,
+            mustResolve = true,
+            allowPromotionAndDemotion = false,
+            allowFluent = false
+        )
     }
 
     @Suppress("LongParameterList")
@@ -4250,11 +4064,11 @@ class Cql2ElmVisitor(
         allowPromotionAndDemotion: Boolean,
         allowFluent: Boolean
     ): Expression? {
-        var functionName = functionName
+        var name = functionName
         if (allowFluent) {
             libraryBuilder.checkCompatibilityLevel("Fluent functions", "1.5")
         }
-        functionName = ensureSystemFunctionName(libraryName, functionName)
+        name = ensureSystemFunctionName(libraryName, name)
 
         // 1. Ensure all overloads of the function are registered with the operator map
         // 2. Resolve the function, allowing for the case that operator map is a
@@ -4266,7 +4080,7 @@ class Cql2ElmVisitor(
         // Find all functionDefinitionInfo instances with the given name
         // register each functionDefinitionInfo
         if (libraryName == null || libraryName == "" || libraryName == libraryInfo.libraryName) {
-            val fdis = libraryInfo.resolveFunctionReference(functionName)
+            val fdis = libraryInfo.resolveFunctionReference(name)
             if (fdis != null) {
                 for ((_, context, definition) in fdis) {
                     val saveContext = saveCurrentContext(context)
@@ -4281,34 +4095,33 @@ class Cql2ElmVisitor(
         val result =
             libraryBuilder.resolveFunction(
                 libraryName,
-                functionName,
+                name,
                 expressions,
                 mustResolve,
                 allowPromotionAndDemotion,
                 allowFluent
             )
-        if (result is FunctionRefInvocation) {
-            if (
+        if (
+            result is FunctionRefInvocation &&
                 result.resolution != null &&
-                    (result.resolution!!.operator.libraryName == null ||
-                        (result.resolution!!.operator.libraryName ==
-                            libraryBuilder.compiledLibrary.identifier!!.id))
-            ) {
-                val op = result.resolution!!.operator
-                val fh = getFunctionHeader(op)
-                if (!fh.isCompiled) {
-                    val ctx = getFunctionDefinitionContext(fh)
-                    val saveContext = saveCurrentContext(fh.functionDef.context!!)
-                    val saveChunks = chunks
-                    chunks = Stack()
-                    try {
-                        val fd = compileFunctionDefinition(ctx)
-                        op.resultType = fd.resultType
-                        result.resultType = op.resultType
-                    } finally {
-                        currentContext = saveContext
-                        chunks = saveChunks
-                    }
+                (result.resolution!!.operator.libraryName == null ||
+                    (result.resolution!!.operator.libraryName ==
+                        libraryBuilder.compiledLibrary.identifier!!.id))
+        ) {
+            val op = result.resolution!!.operator
+            val fh = getFunctionHeader(op)
+            if (!fh.isCompiled) {
+                val ctx = getFunctionDefinitionContext(fh)
+                val saveContext = saveCurrentContext(fh.functionDef.context!!)
+                val saveChunks = chunks
+                chunks = Stack()
+                try {
+                    val fd = compileFunctionDefinition(ctx)
+                    op.resultType = fd.resultType
+                    result.resultType = op.resultType
+                } finally {
+                    currentContext = saveContext
+                    chunks = saveChunks
                 }
             }
         }
@@ -4324,7 +4137,7 @@ class Cql2ElmVisitor(
         return result?.expression
     }
 
-    fun resolveFunctionOrQualifiedFunction(
+    private fun resolveFunctionOrQualifiedFunction(
         identifier: String,
         paramListCtx: ParamListContext?
     ): Expression? {
@@ -4341,23 +4154,19 @@ class Cql2ElmVisitor(
                 if (isMethodInvocationEnabled) {
                     return systemMethodResolver.resolveMethod(
                         target,
-                        (identifier),
+                        identifier,
                         paramListCtx,
                         true
                     )
                 }
                 if (!isMethodInvocationEnabled) {
                     throw CqlCompilerException(
-                        String.format(
-                            Locale.US,
-                            "The identifier %s could not be resolved as an invocation because method-style invocation is disabled.",
-                            identifier
-                        ),
+                        "The identifier $identifier could not be resolved as an invocation because method-style invocation is disabled.",
                         CqlCompilerException.ErrorSeverity.Error
                     )
                 }
                 throw IllegalArgumentException(
-                    String.format(Locale.US, "Invalid invocation target: %s", target.javaClass.name)
+                    "Invalid invocation target: ${target.javaClass.name}"
                 )
             } finally {
                 libraryBuilder.pushExpressionTarget(target)
@@ -4369,7 +4178,7 @@ class Cql2ElmVisitor(
         val thisRef: Expression? = libraryBuilder.resolveIdentifier("\$this", false)
         if (thisRef != null) {
             val result: Expression? =
-                systemMethodResolver.resolveMethod(thisRef, (identifier), paramListCtx, false)
+                systemMethodResolver.resolveMethod(thisRef, identifier, paramListCtx, false)
             if (result != null) {
                 return result
             }
@@ -4381,7 +4190,7 @@ class Cql2ElmVisitor(
         val parameterRef: ParameterRef? = libraryBuilder.resolveImplicitContext()
         if (parameterRef != null) {
             val result: Expression? =
-                systemMethodResolver.resolveMethod(parameterRef, (identifier), paramListCtx, false)
+                systemMethodResolver.resolveMethod(parameterRef, identifier, paramListCtx, false)
             if (result != null) {
                 return result
             }
@@ -4445,18 +4254,10 @@ class Cql2ElmVisitor(
                     }
                 }
                 if (signaturesMatch) {
-                    target =
-                        if (target == null) {
-                            fd
-                        } else {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Internal error attempting to resolve function header for %s",
-                                    op.name
-                                )
-                            )
-                        }
+                    check(target == null) {
+                        "Internal error attempting to resolve function header for ${op.name}"
+                    }
+                    target = fd
                 }
             }
         }
@@ -4480,52 +4281,36 @@ class Cql2ElmVisitor(
         val fd =
             getFunctionDef(op)
                 ?: throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Could not resolve function header for operator %s",
-                        op.name
-                    )
+                    "Could not resolve function header for operator ${op.name}"
                 )
         return getFunctionHeaderByDef(fd)
             ?: throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Could not resolve function header for operator %s",
-                    op.name
-                )
+                "Could not resolve function header for operator ${op.name}"
             )
     }
 
     private fun getFunctionDefinitionContext(fh: FunctionHeader): FunctionDefinitionContext {
         return functionDefinitions[fh]
             ?: throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Could not resolve function definition context for function header %s",
-                    fh.functionDef.name
-                )
+                "Could not resolve function definition context for function header ${fh.functionDef.name}"
             )
     }
 
-    fun registerFunctionDefinition(ctx: FunctionDefinitionContext) {
+    private fun registerFunctionDefinition(ctx: FunctionDefinitionContext) {
         val fh = getFunctionHeader(ctx)
         if (!libraryBuilder.compiledLibrary.contains(fh.functionDef)) {
             libraryBuilder.addExpression(fh.functionDef)
         }
     }
 
-    fun compileFunctionDefinition(ctx: FunctionDefinitionContext): FunctionDef {
+    private fun compileFunctionDefinition(ctx: FunctionDefinitionContext): FunctionDef {
         val fh: FunctionHeader = getFunctionHeader(ctx)
         val functionDef: FunctionDef = fh.functionDef
         val resultType: TypeSpecifier? = fh.resultType
         val op: Operator =
             libraryBuilder.resolveFunctionDefinition(fh.functionDef)
                 ?: throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Internal error: Could not resolve operator map entry for function header %s",
-                        fh.mangledName
-                    )
+                    "Internal error: Could not resolve operator map entry for function header ${fh.mangledName}"
                 )
         libraryBuilder.pushIdentifier(functionDef.name!!, functionDef, IdentifierScope.GLOBAL)
         val operand = op.functionDef!!.operand as List<OperandDef>
@@ -4555,17 +4340,9 @@ class Cql2ElmVisitor(
                         (functionDef.expression != null) &&
                         (functionDef.expression!!.resultType != null)
                 ) {
-                    if (!subTypeOf(functionDef.expression!!.resultType, resultType.resultType)) {
+                    require(subTypeOf(functionDef.expression!!.resultType, resultType.resultType)) {
                         // ERROR:
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Function %s has declared return type %s but the function body returns incompatible type %s.",
-                                functionDef.name,
-                                resultType.resultType,
-                                functionDef.expression!!.resultType
-                            )
-                        )
+                        "Function ${functionDef.name} has declared return type ${resultType.resultType} but the function body returns incompatible type ${functionDef.expression!!.resultType}."
                     }
                 }
                 functionDef.resultType = functionDef.expression!!.resultType
@@ -4574,11 +4351,7 @@ class Cql2ElmVisitor(
                 functionDef.external = true
                 requireNotNull(resultType) {
                     // ERROR:
-                    String.format(
-                        Locale.US,
-                        "Function %s is marked external but does not declare a return type.",
-                        functionDef.name
-                    )
+                    "Function ${functionDef.name} is marked external but does not declare a return type."
                 }
                 functionDef.resultType = resultType.resultType
                 op.resultType = functionDef.resultType
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlCompiler.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlCompiler.kt
index 8070a5597..f9d51fcdf 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlCompiler.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlCompiler.kt
@@ -68,9 +68,6 @@ class CqlCompiler(
         return retrieves
     }
 
-    val compiledLibraries: Map<VersionedIdentifier, CompiledLibrary>
-        get() = libraryManager.compiledLibraries
-
     val libraries: Map<VersionedIdentifier, Library>
         get() {
             val result = HashMap<VersionedIdentifier, Library>()
@@ -129,11 +126,7 @@ class CqlCompiler(
             } else {
                 if (offendingSymbol is CommonToken) {
                     builder.recordParsingException(
-                        CqlSyntaxException(
-                            String.format(Locale.US, "Syntax error at %s", offendingSymbol.text),
-                            trackback,
-                            e
-                        )
+                        CqlSyntaxException("Syntax error at ${offendingSymbol.text}", trackback, e)
                     )
                 } else {
                     builder.recordParsingException(CqlSyntaxException("Syntax error", trackback, e))
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlInternalException.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlInternalException.kt
index 8369a8bb0..4458fc36c 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlInternalException.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlInternalException.kt
@@ -3,19 +3,5 @@ package org.cqframework.cql.cql2elm
 import org.cqframework.cql.cql2elm.tracking.TrackBack
 
 /** Created by Bryn on 5/20/2017. */
-class CqlInternalException : CqlCompilerException {
-    constructor(message: String?) : super(message, ErrorSeverity.Error)
-
-    constructor(message: String?, cause: Throwable?) : super(message, ErrorSeverity.Error, cause)
-
-    constructor(
-        message: String?,
-        locator: TrackBack?
-    ) : super(message, ErrorSeverity.Error, locator)
-
-    constructor(
-        message: String?,
-        locator: TrackBack?,
-        cause: Throwable?
-    ) : super(message, ErrorSeverity.Error, locator, cause)
-}
+class CqlInternalException(message: String?, locator: TrackBack? = null, cause: Throwable? = null) :
+    CqlCompilerException(message, ErrorSeverity.Error, locator, cause)
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSemanticException.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSemanticException.kt
index f48aa6ac9..5e8406c61 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSemanticException.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSemanticException.kt
@@ -6,18 +6,6 @@ import org.cqframework.cql.cql2elm.tracking.TrackBack
 class CqlSemanticException : CqlCompilerException {
     constructor(message: String?) : super(message)
 
-    constructor(message: String?, severity: ErrorSeverity) : super(message, severity)
-
-    constructor(message: String?, cause: Throwable?) : super(message, cause)
-
-    constructor(
-        message: String?,
-        severity: ErrorSeverity,
-        cause: Throwable?
-    ) : super(message, severity, cause)
-
-    constructor(message: String?, locator: TrackBack?) : super(message, locator)
-
     constructor(
         message: String?,
         severity: ErrorSeverity,
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSyntaxException.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSyntaxException.kt
index f0cfca952..0f23747db 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSyntaxException.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlSyntaxException.kt
@@ -3,37 +3,5 @@ package org.cqframework.cql.cql2elm
 import org.cqframework.cql.cql2elm.tracking.TrackBack
 
 /** Created by Bryn on 3/27/2017. */
-class CqlSyntaxException : CqlCompilerException {
-    constructor(message: String?) : super(message)
-
-    constructor(message: String?, severity: ErrorSeverity) : super(message, severity)
-
-    constructor(message: String?, cause: Throwable?) : super(message, cause)
-
-    constructor(
-        message: String?,
-        severity: ErrorSeverity,
-        cause: Throwable?
-    ) : super(message, severity, cause)
-
-    constructor(message: String?, locator: TrackBack?) : super(message, locator)
-
-    constructor(
-        message: String?,
-        severity: ErrorSeverity,
-        locator: TrackBack?
-    ) : super(message, severity, locator)
-
-    constructor(
-        message: String?,
-        locator: TrackBack?,
-        cause: Throwable?
-    ) : super(message, locator, cause)
-
-    constructor(
-        message: String?,
-        severity: ErrorSeverity,
-        locator: TrackBack?,
-        cause: Throwable?
-    ) : super(message, severity, locator, cause)
-}
+class CqlSyntaxException(message: String?, locator: TrackBack?, cause: Throwable?) :
+    CqlCompilerException(message, locator, cause)
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlTranslator.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlTranslator.kt
index 7476b1cdf..ba91c64dd 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlTranslator.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/CqlTranslator.kt
@@ -73,9 +73,6 @@ class CqlTranslator(
     val libraries: Map<VersionedIdentifier, Library?>
         get() = compiler.libraries
 
-    val translatedLibraries: Map<VersionedIdentifier, CompiledLibrary?>
-        get() = compiler.compiledLibraries
-
     val exceptions: List<CqlCompilerException?>?
         // public Map<String, String> getLibrariesAsXML() {
         get() = compiler.exceptions
@@ -97,35 +94,6 @@ class CqlTranslator(
             return CqlTranslator(null, null, CharStreams.fromString(cqlText), libraryManager)
         }
 
-        @JvmStatic
-        fun fromText(
-            namespaceInfo: NamespaceInfo?,
-            cqlText: String,
-            libraryManager: LibraryManager
-        ): CqlTranslator {
-            return CqlTranslator(
-                namespaceInfo,
-                null,
-                CharStreams.fromString(cqlText),
-                libraryManager
-            )
-        }
-
-        @JvmStatic
-        fun fromText(
-            namespaceInfo: NamespaceInfo?,
-            sourceInfo: VersionedIdentifier?,
-            cqlText: String,
-            libraryManager: LibraryManager
-        ): CqlTranslator {
-            return CqlTranslator(
-                namespaceInfo,
-                sourceInfo,
-                CharStreams.fromString(cqlText),
-                libraryManager
-            )
-        }
-
         @JvmStatic
         @Throws(IOException::class)
         fun fromStream(
@@ -220,7 +188,7 @@ class CqlTranslator(
         fun fromFile(
             namespaceInfo: NamespaceInfo?,
             sourceInfo: VersionedIdentifier?,
-            cqlFile: File?,
+            cqlFile: File,
             libraryManager: LibraryManager
         ): CqlTranslator {
             return CqlTranslator(
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DataTypes.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DataTypes.kt
index 7d533bd1c..dd0eebe57 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DataTypes.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DataTypes.kt
@@ -1,23 +1,18 @@
 package org.cqframework.cql.cql2elm
 
-import java.util.*
 import org.hl7.cql.model.DataType
 
+private const val UNKNOWN = "<unknown>"
+
 object DataTypes {
-    @JvmStatic
     fun verifyType(actualType: DataType?, expectedType: DataType?) {
         require(subTypeOf(actualType, expectedType)) {
             // ERROR:
-            String.format(
-                Locale.US,
-                "Expected an expression of type '%s', but found an expression of type '%s'.",
-                if (expectedType != null) expectedType.toLabel() else "<unknown>",
-                if (actualType != null) actualType.toLabel() else "<unknown>"
-            )
+            "Expected an expression of type '${expectedType?.toLabel() ?: UNKNOWN}'," +
+                "but found an expression of type '${actualType?.toLabel() ?: UNKNOWN}'."
         }
     }
 
-    @JvmStatic
     fun verifyCast(targetType: DataType?, sourceType: DataType?) {
         // Casting can be used for compatible types as well as subtypes and supertypes
         require(
@@ -26,30 +21,24 @@ object DataTypes {
                 compatibleWith(sourceType, targetType)
         ) {
             // ERROR:
-            String.format(
-                Locale.US,
-                "Expression of type '%s' cannot be cast as a value of type '%s'.",
-                if (sourceType != null) sourceType.toLabel() else "<unknown>",
-                if (targetType != null) targetType.toLabel() else "<unknown>"
-            )
+            "Expression of type '${sourceType?.toLabel() ?: UNKNOWN}'" +
+                " cannot be cast as a value of type '${targetType?.toLabel() ?: UNKNOWN}'."
         }
     }
 
-    @JvmStatic
     fun equal(a: DataType?, b: DataType?): Boolean {
         return a != null && b != null && a == b
     }
 
-    fun compatibleWith(a: DataType?, b: DataType?): Boolean {
+    private fun compatibleWith(a: DataType?, b: DataType?): Boolean {
         return a != null && b != null && a.isCompatibleWith(b)
     }
 
-    @JvmStatic
     fun subTypeOf(a: DataType?, b: DataType?): Boolean {
         return a != null && b != null && a.isSubTypeOf(b)
     }
 
-    fun superTypeOf(a: DataType?, b: DataType?): Boolean {
+    private fun superTypeOf(a: DataType?, b: DataType?): Boolean {
         return a != null && b != null && a.isSuperTypeOf(b)
     }
 }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceLoader.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceLoader.kt
index 2d50a776a..3353e4f24 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceLoader.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceLoader.kt
@@ -2,7 +2,6 @@ package org.cqframework.cql.cql2elm
 
 import java.io.InputStream
 import java.nio.file.Path
-import java.util.*
 import kotlin.collections.ArrayList
 import org.hl7.cql.model.NamespaceAware
 import org.hl7.cql.model.NamespaceManager
@@ -10,12 +9,12 @@ import org.hl7.elm.r1.VersionedIdentifier
 
 /**
  * Used by LibraryManager to manage a set of library source providers that resolve library includes
- * within CQL. Package private since its not intended to be used outside the context of the
+ * within CQL. Package private since it's not intended to be used outside the context of the
  * instantiating LibraryManager instance.
  */
 internal class DefaultLibrarySourceLoader : LibrarySourceLoader, NamespaceAware, PathAware {
     private val providers: MutableList<LibrarySourceProvider> = ArrayList()
-    var initialized: Boolean = false
+    private var initialized: Boolean = false
 
     override fun registerProvider(provider: LibrarySourceProvider) {
         if (namespaceManager != null && provider is NamespaceAware) {
@@ -30,9 +29,7 @@ internal class DefaultLibrarySourceLoader : LibrarySourceLoader, NamespaceAware,
     private var path: Path? = null
 
     override fun setPath(path: Path) {
-        require(path.toFile().isDirectory) {
-            String.format(Locale.US, "path '%s' is not a valid directory", path)
-        }
+        require(path.toFile().isDirectory) { "path '$path' is not a valid directory" }
 
         this.path = path
         for (provider in getProviders()) {
@@ -65,25 +62,13 @@ internal class DefaultLibrarySourceLoader : LibrarySourceLoader, NamespaceAware,
             val localSource: InputStream? = provider.getLibrarySource(libraryIdentifier)
             if (localSource != null) {
                 require(source == null) {
-                    String.format(
-                        Locale.US,
-                        "Multiple sources found for library %s, version %s.",
-                        libraryIdentifier.id,
-                        libraryIdentifier.version
-                    )
+                    "Multiple sources found for library ${libraryIdentifier.id}, version ${libraryIdentifier.version}."
                 }
                 source = localSource
             }
         }
-        if (source == null) {
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Could not load source for library %s, version %s.",
-                    libraryIdentifier.id,
-                    libraryIdentifier.version
-                )
-            )
+        requireNotNull(source) {
+            "Could not load source for library ${libraryIdentifier.id}, version ${libraryIdentifier.version}."
         }
         return source
     }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceProvider.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceProvider.kt
index 2a61e3e81..506110290 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceProvider.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultLibrarySourceProvider.kt
@@ -4,7 +4,6 @@ package org.cqframework.cql.cql2elm
 
 import java.io.*
 import java.nio.file.Path
-import java.util.*
 import org.cqframework.cql.cql2elm.model.Version
 import org.hl7.elm.r1.VersionedIdentifier
 
@@ -22,9 +21,7 @@ class DefaultLibrarySourceProvider(path: Path) : LibrarySourceProvider, PathAwar
     }
 
     override fun setPath(path: Path) {
-        require(path.toFile().isDirectory) {
-            String.format(Locale.US, "path '%s' is not a valid directory", path)
-        }
+        require(path.toFile().isDirectory) { "path '$path' is not a valid directory" }
         this.path = path
     }
 
@@ -35,17 +32,14 @@ class DefaultLibrarySourceProvider(path: Path) : LibrarySourceProvider, PathAwar
             val libraryName: String = libraryIdentifier.id!!
             val libraryPath: Path =
                 currentPath.resolve(
-                    String.format(
-                        Locale.US,
-                        "%s%s.cql",
-                        libraryName,
+                    "$libraryName${
                         if (libraryIdentifier.version != null) ("-" + libraryIdentifier.version)
                         else ""
-                    )
+                    }.cql"
                 )
             var libraryFile: File? = libraryPath.toFile()
             if (libraryFile?.exists() != true) {
-                val filter = FilenameFilter { path, name ->
+                val filter = FilenameFilter { _, name ->
                     name.startsWith(libraryName) && name.endsWith(".cql")
                 }
                 var mostRecentFile: File? = null
@@ -53,7 +47,7 @@ class DefaultLibrarySourceProvider(path: Path) : LibrarySourceProvider, PathAwar
                 val requestedVersion: Version? =
                     if (libraryIdentifier.version == null) null
                     else Version(libraryIdentifier.version!!)
-                for (file: File in currentPath.toFile().listFiles(filter)) {
+                for (file: File in currentPath.toFile().listFiles(filter)!!) {
                     var fileName: String = file.name
                     val indexOfExtension: Int = fileName.lastIndexOf(".")
                     if (indexOfExtension >= 0) {
@@ -72,9 +66,9 @@ class DefaultLibrarySourceProvider(path: Path) : LibrarySourceProvider, PathAwar
                             @Suppress("ComplexCondition")
                             if (
                                 (mostRecent == null ||
-                                    (((version.isComparable) &&
+                                    ((version.isComparable) &&
                                         (mostRecent.isComparable) &&
-                                        (version.compareTo(mostRecent) > 0))))
+                                        (version > mostRecent)))
                             ) {
                                 mostRecent = version
                                 mostRecentFile = file
@@ -106,11 +100,7 @@ class DefaultLibrarySourceProvider(path: Path) : LibrarySourceProvider, PathAwar
                 }
             } catch (e: FileNotFoundException) {
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Could not load source for library %s.",
-                        libraryIdentifier.id
-                    ),
+                    "Could not load source for library ${libraryIdentifier.id}.",
                     e
                 )
             }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultModelInfoProvider.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultModelInfoProvider.kt
index e998794b1..caa0541a8 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultModelInfoProvider.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/DefaultModelInfoProvider.kt
@@ -4,7 +4,6 @@ package org.cqframework.cql.cql2elm
 
 import java.io.*
 import java.nio.file.Path
-import java.util.*
 import org.cqframework.cql.cql2elm.model.Version
 import org.hl7.cql.model.ModelIdentifier
 import org.hl7.cql.model.ModelInfoProvider
@@ -17,19 +16,15 @@ import org.hl7.elm_modelinfo.r1.serializing.ModelInfoReaderFactory
 // form
 // <major>[.<minor>[.<patch>]]
 // Usage outside these boundaries will result in errors or incorrect behavior.
-class DefaultModelInfoProvider : ModelInfoProvider, PathAware {
-    constructor()
-
-    constructor(path: Path) {
+class DefaultModelInfoProvider() : ModelInfoProvider, PathAware {
+    constructor(path: Path) : this() {
         this.setPath(path)
     }
 
     private var path: Path? = null
 
     override fun setPath(path: Path) {
-        require(path.toFile().isDirectory) {
-            String.format(Locale.US, "path '%s' is not a valid directory", path)
-        }
+        require(path.toFile().isDirectory) { "path '$path' is not a valid directory" }
         this.path = path
     }
 
@@ -48,24 +43,18 @@ class DefaultModelInfoProvider : ModelInfoProvider, PathAware {
             val modelVersion = modelIdentifier.version
             val modelPath =
                 currentPath.resolve(
-                    String.format(
-                        Locale.US,
-                        "%s-modelinfo%s.xml",
-                        modelName.lowercase(Locale.getDefault()),
-                        if (modelVersion != null) "-$modelVersion" else ""
-                    )
+                    "${modelName.lowercase()}-modelinfo${if (modelVersion != null) "-$modelVersion" else ""}.xml"
                 )
-            var modelFile: File? = modelPath.toFile()
-            if (modelFile?.exists() != true) {
-                val filter = FilenameFilter { path, name ->
-                    name.startsWith(modelName.lowercase(Locale.getDefault()) + "-modelinfo") &&
-                        name.endsWith(".xml")
+            var modelFile = modelPath.toFile()
+            if (!modelFile.exists()) {
+                val filter = FilenameFilter { _, name ->
+                    name.startsWith(modelName.lowercase() + "-modelinfo") && name.endsWith(".xml")
                 }
                 var mostRecentFile: File? = null
                 var mostRecent: Version? = null
                 try {
                     val requestedVersion = if (modelVersion == null) null else Version(modelVersion)
-                    for (file in currentPath.toFile().listFiles(filter)) {
+                    for (file in currentPath.toFile().listFiles(filter)!!) {
                         var fileName = file.name
                         val indexOfExtension = fileName.lastIndexOf(".")
                         if (indexOfExtension >= 0) {
@@ -87,7 +76,7 @@ class DefaultModelInfoProvider : ModelInfoProvider, PathAware {
                                     mostRecent == null ||
                                         version.isComparable &&
                                             mostRecent.isComparable &&
-                                            version.compareTo(mostRecent) > 0
+                                            version > mostRecent
                                 ) {
                                     mostRecent = version
                                     mostRecentFile = file
@@ -102,7 +91,7 @@ class DefaultModelInfoProvider : ModelInfoProvider, PathAware {
                             }
                         }
                     }
-                    modelFile = mostRecentFile
+                    modelFile = mostRecentFile!!
                 } catch (@Suppress("SwallowedException") e: IllegalArgumentException) {
                     // do nothing, if the version can't be understood as a semantic version, don't
                     // allow unspecified
@@ -114,11 +103,7 @@ class DefaultModelInfoProvider : ModelInfoProvider, PathAware {
                 return ModelInfoReaderFactory.getReader("application/xml")?.read(inputStream)
             } catch (e: IOException) {
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Could not load definition for model info %s.",
-                        modelIdentifier.id
-                    ),
+                    "Could not load definition for model info ${modelIdentifier.id}.",
                     e
                 )
             }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryBuilder.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryBuilder.kt
index c316c036d..98214d638 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryBuilder.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryBuilder.kt
@@ -17,6 +17,8 @@ import org.hl7.cql_annotations.r1.*
 import org.hl7.cql_annotations.r1.ObjectFactory
 import org.hl7.elm.r1.*
 
+private const val FP_THIS = "\$this"
+
 /** Created by Bryn on 12/29/2016. */
 @Suppress("LargeClass", "TooManyFunctions", "ForbiddenComment", "ReturnCount", "MaxLineLength")
 class LibraryBuilder(
@@ -32,7 +34,7 @@ class LibraryBuilder(
         None,
 
         /*
-        Indicates signatures will only be included in invocations if the declared signature of the resolve operator is different than the invocation signature
+        Indicates signatures will only be included in invocations if the declared signature of the resolve operator is different from the invocation signature
          */
         Differing,
 
@@ -69,8 +71,7 @@ class LibraryBuilder(
         MutableMap<String, ResultWithPossibleError<NamedTypeSpecifier?>> =
         HashMap()
     private val libraries: MutableMap<String, CompiledLibrary> = LinkedHashMap()
-    private val systemFunctionResolver: SystemFunctionResolver =
-        SystemFunctionResolver(this, objectFactory)
+    private val systemFunctionResolver: SystemFunctionResolver = SystemFunctionResolver(this)
     private val expressionContext = Stack<String>()
     private val expressionDefinitions = ExpressionDefinitionContextStack()
     private val functionDefs = Stack<FunctionDef>()
@@ -170,13 +171,7 @@ class LibraryBuilder(
             "Internal Translator Error: feature name is required to perform a compatibility check"
         }
         require(isCompatibleWith(sinceCompatibilityLevel)) {
-            String.format(
-                Locale.US,
-                "Feature %s was introduced in version %s and so cannot be used at compatibility level %s",
-                featureName,
-                sinceCompatibilityLevel,
-                compatibilityLevel
-            )
+            "Feature $featureName was introduced in version $sinceCompatibilityLevel and so cannot be used at compatibility level $compatibilityLevel"
         }
     }
 
@@ -213,18 +208,10 @@ class LibraryBuilder(
             // Add the model using def to the output
             buildUsingDef(modelIdentifier, model, localIdentifier)
         }
-        if (
-            (modelIdentifier.version != null && modelIdentifier.version != model.modelInfo.version)
+        require(
+            !(modelIdentifier.version != null && modelIdentifier.version != model.modelInfo.version)
         ) {
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Could not load model information for model %s, version %s because version %s is already loaded.",
-                    modelIdentifier.id,
-                    modelIdentifier.version,
-                    model.modelInfo.version
-                )
-            )
+            "Could not load model information for model ${modelIdentifier.id}, version ${modelIdentifier.version} because version ${model.modelInfo.version} is already loaded."
         }
         return model
     }
@@ -284,22 +271,14 @@ class LibraryBuilder(
     }
 
     @Suppress("NestedBlockDepth")
-    fun resolveLabel(modelName: String?, label: String): ClassType? {
+    private fun resolveLabel(modelName: String?, label: String): ClassType? {
         var result: ClassType? = null
         if (modelName == null || (modelName == "")) {
             for (model: Model? in models.values) {
                 val modelResult: ClassType? = model!!.resolveLabel(label)
                 if (modelResult != null) {
-                    if (result != null) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Label %s is ambiguous between %s and %s.",
-                                label,
-                                result.label,
-                                modelResult.label
-                            )
-                        )
+                    require(result == null) {
+                        "Label $label is ambiguous between ${(result as ClassType).label} and ${modelResult.label}."
                     }
                     result = modelResult
                 }
@@ -327,16 +306,8 @@ class LibraryBuilder(
             for (model: Model? in models.values) {
                 val modelResult: ModelContext? = model!!.resolveContextName(contextName)
                 if (modelResult != null) {
-                    if (result != null) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Context name %s is ambiguous between %s and %s.",
-                                contextName,
-                                result.name,
-                                modelResult.name
-                            )
-                        )
+                    require(result == null) {
+                        "Context name $contextName is ambiguous between ${(result as ModelContext).name} and ${modelResult.name}."
                     }
                     result = modelResult
                 }
@@ -369,16 +340,8 @@ class LibraryBuilder(
                 for (model: Model? in models.values) {
                     val modelResult: DataType? = model!!.resolveTypeName(typeName)
                     if (modelResult != null) {
-                        if (result != null) {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Type name %s is ambiguous between %s and %s.",
-                                    typeName,
-                                    (result as NamedType).name,
-                                    (modelResult as NamedType).name
-                                )
-                            )
+                        require(result == null) {
+                            "Type name $typeName is ambiguous between ${(result as NamedType).name} and ${(modelResult as NamedType).name}."
                         }
                         result = modelResult
                     }
@@ -401,15 +364,8 @@ class LibraryBuilder(
                     // This really should be
                     // being done with preprocessor directives,
                     // but that's a whole other project in and of itself.
-                    if (!isCompatibleWith("1.5") && !isFHIRHelpers(compiledLibrary)) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "The type %s was introduced in CQL 1.5 and cannot be referenced at compatibility level %s",
-                                (result as NamedType).name,
-                                compatibilityLevel
-                            )
-                        )
+                    require(!(!isCompatibleWith("1.5") && !isFHIRHelpers(compiledLibrary))) {
+                        "The type ${(result as NamedType).name} was introduced in CQL 1.5 and cannot be referenced at compatibility level $compatibilityLevel"
                     }
             }
         }
@@ -430,7 +386,7 @@ class LibraryBuilder(
         // simpleTypeSpecifier: (identifier '.')? identifier
         // intervalTypeSpecifier: 'interval' '<' typeSpecifier '>'
         // listTypeSpecifier: 'list' '<' typeSpecifier '>'
-        when {
+        return when {
             typeSpecifier.lowercase(Locale.getDefault()).startsWith("interval<") -> {
                 val pointType =
                     resolveTypeSpecifier(
@@ -439,10 +395,10 @@ class LibraryBuilder(
                             typeSpecifier.lastIndexOf('>')
                         )
                     )
-                return IntervalType(pointType!!)
+                IntervalType(pointType!!)
             }
             else ->
-                return if (typeSpecifier.lowercase(Locale.getDefault()).startsWith("list<")) {
+                if (typeSpecifier.lowercase(Locale.getDefault()).startsWith("list<")) {
                     val elementType =
                         resolveTypeName(
                             typeSpecifier.substring(
@@ -475,13 +431,11 @@ class LibraryBuilder(
             // Special case for FHIR-derived models that include FHIR Helpers
             return modelManager.resolveModelByUri("http://hl7.org/fhir")
         }
-        requireNotNull(usingDef) {
-            String.format(Locale.US, "Could not resolve model name %s", modelName)
-        }
+        requireNotNull(usingDef) { "Could not resolve model name $modelName" }
         return getModel(usingDef)
     }
 
-    fun getModel(usingDef: UsingDef): Model {
+    private fun getModel(usingDef: UsingDef): Model {
         return getModel(
             ModelIdentifier(
                 id = NamespaceManager.getNamePart(usingDef.uri)!!,
@@ -504,7 +458,7 @@ class LibraryBuilder(
         }
     }
 
-    val systemLibrary: CompiledLibrary
+    private val systemLibrary: CompiledLibrary
         get() = resolveLibrary("System")
 
     fun resolveLibrary(identifier: String?): CompiledLibrary {
@@ -512,15 +466,13 @@ class LibraryBuilder(
             checkLiteralContext()
         }
         return libraries[identifier]
-            ?: throw IllegalArgumentException(
-                String.format(Locale.US, "Could not resolve library name %s.", identifier)
-            )
+            ?: throw IllegalArgumentException("Could not resolve library name $identifier.")
     }
 
     fun resolveNamespaceUri(namespaceName: String, mustResolve: Boolean): String? {
         val namespaceUri = libraryManager.namespaceManager.resolveNamespaceUri(namespaceName)
         require(!(namespaceUri == null && mustResolve)) {
-            String.format(Locale.US, "Could not resolve namespace name %s", namespaceName)
+            "Could not resolve namespace name $namespaceName"
         }
         return namespaceUri
     }
@@ -566,10 +518,7 @@ class LibraryBuilder(
                     errorSeverity == CqlCompilerException.ErrorSeverity.Error)
             CqlCompilerException.ErrorSeverity.Error ->
                 errorSeverity == CqlCompilerException.ErrorSeverity.Error
-            else ->
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Unknown error severity %s", errorSeverity.toString())
-                )
+            else -> throw IllegalArgumentException("Unknown error severity $errorSeverity")
         }
     }
 
@@ -610,22 +559,8 @@ class LibraryBuilder(
         }
     }
 
-    private val libraryName: String
-        get() {
-            var libraryName = library.identifier!!.id
-            if (libraryName == null) {
-                libraryName = "Anonymous"
-            }
-            if (library.identifier!!.system != null) {
-                libraryName = library.identifier!!.system + "/" + libraryName
-            }
-            return libraryName
-        }
-
     fun beginTranslation() {
         loadSystemLibrary()
-
-        // libraryManager.beginCompilation(getLibraryName());
     }
 
     var libraryIdentifier: VersionedIdentifier?
@@ -637,7 +572,6 @@ class LibraryBuilder(
 
     fun endTranslation() {
         applyTargetModelMaps()
-        // libraryManager.endCompilation(getLibraryName());
     }
 
     fun canResolveLibrary(includeDef: IncludeDef): Boolean {
@@ -671,7 +605,7 @@ class LibraryBuilder(
 
         // Note that translation of a referenced library may result in implicit specification of the
         // namespace
-        // In this case, the referencedLibrary will have a namespaceUri different than the currently
+        // In this case, the referencedLibrary will have a namespaceUri different from the currently
         // resolved
         // namespaceUri
         // of the IncludeDef.
@@ -758,7 +692,7 @@ class LibraryBuilder(
         return compiledLibrary.resolveIncludeRef(identifier)
     }
 
-    fun resolveIncludeAlias(libraryIdentifier: VersionedIdentifier): String? {
+    private fun resolveIncludeAlias(libraryIdentifier: VersionedIdentifier): String? {
         return compiledLibrary.resolveIncludeAlias(libraryIdentifier)
     }
 
@@ -812,8 +746,8 @@ class LibraryBuilder(
             libraryName,
             operatorName,
             UnaryExpressionInvocation(expression),
-            false,
-            false
+            allowPromotionAndDemotion = false,
+            allowFluent = false
         )
     }
 
@@ -871,8 +805,8 @@ class LibraryBuilder(
             libraryName,
             operatorName,
             TernaryExpressionInvocation(expression),
-            false,
-            false
+            allowPromotionAndDemotion = false,
+            allowFluent = false
         )
     }
 
@@ -885,8 +819,8 @@ class LibraryBuilder(
             libraryName,
             operatorName,
             NaryExpressionInvocation(expression!!),
-            false,
-            false
+            allowPromotionAndDemotion = false,
+            allowFluent = false
         )
     }
 
@@ -899,8 +833,8 @@ class LibraryBuilder(
             libraryName,
             operatorName,
             AggregateExpressionInvocation(expression),
-            false,
-            false
+            allowPromotionAndDemotion = false,
+            allowFluent = false
         )
     }
 
@@ -1094,7 +1028,7 @@ class LibraryBuilder(
         return result?.expression
     }
 
-    fun resolveInInvocation(
+    private fun resolveInInvocation(
         left: Expression,
         right: Expression,
         dateTimePrecision: DateTimePrecision?
@@ -1113,7 +1047,7 @@ class LibraryBuilder(
         return result?.expression
     }
 
-    fun resolveProperInInvocation(
+    private fun resolveProperInInvocation(
         left: Expression,
         right: Expression,
         dateTimePrecision: DateTimePrecision?
@@ -1132,7 +1066,7 @@ class LibraryBuilder(
         return result?.expression
     }
 
-    fun resolveContainsInvocation(
+    private fun resolveContainsInvocation(
         left: Expression,
         right: Expression,
         dateTimePrecision: DateTimePrecision?
@@ -1151,7 +1085,7 @@ class LibraryBuilder(
         return result?.expression
     }
 
-    fun resolveProperContainsInvocation(
+    private fun resolveProperContainsInvocation(
         left: Expression,
         right: Expression,
         dateTimePrecision: DateTimePrecision?
@@ -1219,11 +1153,23 @@ class LibraryBuilder(
         val includes =
             objectFactory.createIncludes().withOperand(left, right).withPrecision(dateTimePrecision)
         val includesInvocation =
-            resolveBinaryInvocation("System", "Includes", includes, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "Includes",
+                includes,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         val contains =
             objectFactory.createContains().withOperand(left, right).withPrecision(dateTimePrecision)
         val containsInvocation =
-            resolveBinaryInvocation("System", "Contains", contains, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "Contains",
+                contains,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         return lowestScoringInvocation(includesInvocation, containsInvocation)
             ?: resolveBinaryCall("System", "Includes", includes)
 
@@ -1241,14 +1187,26 @@ class LibraryBuilder(
                 .withOperand(left, right)
                 .withPrecision(dateTimePrecision)
         val properIncludesInvocation =
-            resolveBinaryInvocation("System", "ProperIncludes", properIncludes, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "ProperIncludes",
+                properIncludes,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         val properContains =
             objectFactory
                 .createProperContains()
                 .withOperand(left, right)
                 .withPrecision(dateTimePrecision)
         val properContainsInvocation =
-            resolveBinaryInvocation("System", "ProperContains", properContains, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "ProperContains",
+                properContains,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         return lowestScoringInvocation(properIncludesInvocation, properContainsInvocation)
             ?: resolveBinaryCall("System", "ProperIncludes", properIncludes)
 
@@ -1266,10 +1224,23 @@ class LibraryBuilder(
                 .withOperand(left, right)
                 .withPrecision(dateTimePrecision)
         val includedInInvocation =
-            resolveBinaryInvocation("System", "IncludedIn", includedIn, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "IncludedIn",
+                includedIn,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         val inExpression =
             objectFactory.createIn().withOperand(left, right).withPrecision(dateTimePrecision)
-        val inInvocation = resolveBinaryInvocation("System", "In", inExpression, false, false)
+        val inInvocation =
+            resolveBinaryInvocation(
+                "System",
+                "In",
+                inExpression,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         return lowestScoringInvocation(includedInInvocation, inInvocation)
             ?: resolveBinaryCall("System", "IncludedIn", includedIn)
 
@@ -1287,11 +1258,23 @@ class LibraryBuilder(
                 .withOperand(left, right)
                 .withPrecision(dateTimePrecision)
         val properIncludedInInvocation =
-            resolveBinaryInvocation("System", "ProperIncludedIn", properIncludedIn, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "ProperIncludedIn",
+                properIncludedIn,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         val properIn =
             objectFactory.createProperIn().withOperand(left, right).withPrecision(dateTimePrecision)
         val properInInvocation =
-            resolveBinaryInvocation("System", "ProperIn", properIn, false, false)
+            resolveBinaryInvocation(
+                "System",
+                "ProperIn",
+                properIn,
+                mustResolve = false,
+                allowPromotionAndDemotion = false
+            )
         return lowestScoringInvocation(properIncludedInInvocation, properInInvocation)
             ?: resolveBinaryCall("System", "ProperIncludedIn", properIncludedIn)
 
@@ -1303,10 +1286,17 @@ class LibraryBuilder(
         operatorName: String,
         invocation: Invocation
     ): Expression? {
-        return resolveCall(libraryName, operatorName, invocation, true, false, false)
+        return resolveCall(
+            libraryName,
+            operatorName,
+            invocation,
+            mustResolve = true,
+            allowPromotionAndDemotion = false,
+            allowFluent = false
+        )
     }
 
-    fun resolveCall(
+    private fun resolveCall(
         libraryName: String?,
         operatorName: String,
         invocation: Invocation,
@@ -1324,7 +1314,7 @@ class LibraryBuilder(
     }
 
     @Suppress("LongParameterList")
-    fun resolveCall(
+    private fun resolveCall(
         libraryName: String?,
         operatorName: String,
         invocation: Invocation,
@@ -1362,7 +1352,7 @@ class LibraryBuilder(
     }
 
     @Suppress("LongParameterList")
-    fun buildCallContext(
+    private fun buildCallContext(
         libraryName: String?,
         operatorName: String,
         operands: Iterable<Expression?>,
@@ -1373,12 +1363,7 @@ class LibraryBuilder(
         val dataTypes: MutableList<DataType> = ArrayList()
         for (operand in operands) {
             require(!(operand == null || operand.resultType == null)) {
-                String.format(
-                    Locale.US,
-                    "Could not determine signature for invocation of operator %s%s.",
-                    if (libraryName == null) "" else "$libraryName.",
-                    operatorName
-                )
+                "Could not determine signature for invocation of operator ${if (libraryName == null) "" else "$libraryName."}$operatorName."
             }
             dataTypes.add(operand.resultType!!)
         }
@@ -1450,15 +1435,17 @@ class LibraryBuilder(
             // resolution with system functions
             // WARNING:
             reportWarning(
-                String.format(
-                    "The function %s.%s has multiple overloads and due to the SignatureLevel setting (%s), " +
-                        "the overload signature is not being included in the output. This may result in ambiguous function resolution " +
-                        "at runtime, consider setting the SignatureLevel to Overloads or All to ensure that the output includes sufficient " +
-                        "information to support correct overload selection at runtime.",
-                    resolution.operator.libraryName,
-                    resolution.operator.name,
-                    options.signatureLevel.name
-                ),
+                """
+                    The function ${resolution.operator.libraryName}.${resolution.operator.name} has multiple overloads
+                    and due to the SignatureLevel setting (${options.signatureLevel.name}),
+                    the overload signature is not being included in the output.
+                    This may result in ambiguous function resolution
+                    at runtime, consider setting the SignatureLevel to Overloads or All
+                    to ensure that the output includes sufficient
+                    information to support correct overload selection at runtime.
+                """
+                    .trimIndent()
+                    .replace("\n", " "),
                 invocation.expression
             )
         }
@@ -1487,12 +1474,7 @@ class LibraryBuilder(
         val dataTypes: MutableList<DataType> = ArrayList()
         for (operand in fd.operand) {
             requireNotNull(operand.resultType) {
-                String.format(
-                    Locale.US,
-                    "Could not determine signature for invocation of operator %s%s.",
-                    if (libraryName == null) "" else "$libraryName.",
-                    operatorName
-                )
+                "Could not determine signature for invocation of operator ${if (libraryName == null) "" else "$libraryName."}$operatorName."
             }
             dataTypes.add(operand.resultType!!)
         }
@@ -1510,7 +1492,7 @@ class LibraryBuilder(
     }
 
     @Suppress("NestedBlockDepth")
-    fun resolveCall(callContext: CallContext): OperatorResolution? {
+    private fun resolveCall(callContext: CallContext): OperatorResolution? {
         var result: OperatorResolution?
         if (callContext.libraryName.isNullOrEmpty()) {
             result = compiledLibrary.resolveCall(callContext, conversionMap)
@@ -1564,35 +1546,18 @@ class LibraryBuilder(
         } else false
     }
 
-    fun checkOperator(callContext: CallContext, resolution: OperatorResolution?) {
+    private fun checkOperator(callContext: CallContext, resolution: OperatorResolution?) {
         requireNotNull(resolution) {
             // ERROR:
-            String.format(
-                Locale.US,
-                "Could not resolve call to operator %s with signature %s.",
-                callContext.operatorName,
-                callContext.signature
-            )
+            "Could not resolve call to operator ${callContext.operatorName} with signature ${callContext.signature}."
         }
-        if (resolution.operator.fluent && !callContext.allowFluent) {
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Operator %s with signature %s is a fluent function and can only be invoked with fluent syntax.",
-                    callContext.operatorName,
-                    callContext.signature
-                )
-            )
+        require(!(resolution.operator.fluent && !callContext.allowFluent)) {
+            "Operator ${callContext.operatorName} with signature ${callContext.signature} is a fluent function and can only be invoked with fluent syntax."
         }
-        if (callContext.allowFluent && !resolution.operator.fluent && !resolution.allowFluent) {
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Invocation of operator %s with signature %s uses fluent syntax, but the operator is not defined as a fluent function.",
-                    callContext.operatorName,
-                    callContext.signature
-                )
-            )
+        require(
+            !(callContext.allowFluent && !resolution.operator.fluent && !resolution.allowFluent)
+        ) {
+            "Invocation of operator ${callContext.operatorName} with signature ${callContext.signature} uses fluent syntax, but the operator is not defined as a fluent function."
         }
     }
 
@@ -1607,12 +1572,7 @@ class LibraryBuilder(
         ) {
             // ERROR:
             throw CqlSemanticException(
-                String.format(
-                    Locale.US,
-                    "Identifier %s in library %s is marked private and cannot be referenced from another library.",
-                    objectName,
-                    libraryName
-                )
+                "Identifier $objectName in library $libraryName is marked private and cannot be referenced from another library."
             )
         }
     }
@@ -1622,7 +1582,15 @@ class LibraryBuilder(
         functionName: String,
         paramList: List<Expression>
     ): Expression? {
-        return resolveFunction(libraryName, functionName, paramList, true, false, false)?.expression
+        return resolveFunction(
+                libraryName,
+                functionName,
+                paramList,
+                mustResolve = true,
+                allowPromotionAndDemotion = false,
+                allowFluent = false
+            )
+            ?.expression
     }
 
     private fun buildFunctionRef(
@@ -1692,9 +1660,8 @@ class LibraryBuilder(
             functionRef = buildFunctionRef(libraryName, functionName, paramList)
             invocation = FunctionRefInvocation(functionRef)
             if (!allowFluent) {
-                // Only attempt to resolve as a system function if this is not a fluent call or it
-                // is a required
-                // resolution
+                // Only attempt to resolve as a system function if
+                // this is not a fluent call, or it is a required resolution
                 val systemFunction = systemFunctionResolver.resolveSystemFunction(functionRef)
                 if (systemFunction != null) {
                     return systemFunction
@@ -1749,7 +1716,7 @@ class LibraryBuilder(
                     .createAliasedQuerySource()
                     .withAlias("X")
                     .withExpression(expression)
-                    .withResultType(fromType) as AliasedQuerySource
+                    .withResultType(fromType)
             )
             .withReturn(
                 objectFactory
@@ -1760,13 +1727,13 @@ class LibraryBuilder(
                             objectFactory
                                 .createAliasRef()
                                 .withName("X")
-                                .withResultType(fromType.elementType) as AliasRef,
+                                .withResultType(fromType.elementType),
                             conversion.conversion!!
                         )
                     )
-                    .withResultType(toType) as ReturnClause
+                    .withResultType(toType)
             )
-            .withResultType(toType) as Query
+            .withResultType(toType)
     }
 
     private fun reportWarning(message: String, expression: Element?) {
@@ -1843,7 +1810,7 @@ class LibraryBuilder(
     // constructing an
     // interval
     // with null boundaries
-    fun resolveToInterval(expression: Expression?): Expression {
+    private fun resolveToInterval(expression: Expression?): Expression {
         val condition = objectFactory.createIf()
         condition.condition = buildIsNull(expression)
         condition.then = buildNull(IntervalType(expression!!.resultType!!))
@@ -1874,7 +1841,7 @@ class LibraryBuilder(
                         .createProperty()
                         .withSource(expression)
                         .withPath("low")
-                        .withResultType(fromType.pointType) as Property,
+                        .withResultType(fromType.pointType),
                     conversion.conversion!!
                 )
             )
@@ -1883,7 +1850,7 @@ class LibraryBuilder(
                     .createProperty()
                     .withSource(expression)
                     .withPath("lowClosed")
-                    .withResultType(resolveTypeName("System", "Boolean")) as Property
+                    .withResultType(resolveTypeName("System", "Boolean"))
             )
             .withHigh(
                 convertExpression(
@@ -1891,7 +1858,7 @@ class LibraryBuilder(
                         .createProperty()
                         .withSource(expression)
                         .withPath("high")
-                        .withResultType(fromType.pointType) as Property,
+                        .withResultType(fromType.pointType),
                     conversion.conversion
                 )
             )
@@ -1900,13 +1867,13 @@ class LibraryBuilder(
                     .createProperty()
                     .withSource(expression)
                     .withPath("highClosed")
-                    .withResultType(resolveTypeName("System", "Boolean")) as Property
+                    .withResultType(resolveTypeName("System", "Boolean"))
             )
-            .withResultType(toType) as Interval
+            .withResultType(toType)
     }
 
     fun buildAs(expression: Expression?, asType: DataType?): As {
-        val result = objectFactory.createAs().withOperand(expression).withResultType(asType) as As
+        val result = objectFactory.createAs().withOperand(expression).withResultType(asType)
         if (result.resultType is NamedType) {
             result.asType = dataTypeToQName(result.resultType)
         } else {
@@ -1920,7 +1887,7 @@ class LibraryBuilder(
             objectFactory
                 .createIs()
                 .withOperand(expression)
-                .withResultType(resolveTypeName("System", "Boolean")) as Is
+                .withResultType(resolveTypeName("System", "Boolean"))
         if (isType is NamedType) {
             result.isType = dataTypeToQName(isType)
         } else {
@@ -1930,7 +1897,7 @@ class LibraryBuilder(
     }
 
     fun buildNull(nullType: DataType?): Null {
-        val result = objectFactory.createNull().withResultType(nullType) as Null
+        val result = objectFactory.createNull().withResultType(nullType)
         if (nullType is NamedType) {
             result.resultTypeName = dataTypeToQName(nullType)
         } else {
@@ -1939,13 +1906,13 @@ class LibraryBuilder(
         return result
     }
 
-    fun buildIsNull(expression: Expression?): IsNull {
+    private fun buildIsNull(expression: Expression?): IsNull {
         val isNull = objectFactory.createIsNull().withOperand(expression)
         isNull.resultType = resolveTypeName("System", "Boolean")
         return isNull
     }
 
-    fun buildIsNotNull(expression: Expression?): Not {
+    private fun buildIsNotNull(expression: Expression?): Not {
         val isNull = buildIsNull(expression)
         val not = objectFactory.createNot().withOperand(isNull)
         not.resultType = resolveTypeName("System", "Boolean")
@@ -1985,170 +1952,179 @@ class LibraryBuilder(
                 (conversion.fromType.isSuperTypeOf(conversion.toType) ||
                     conversion.fromType.isCompatibleWith(conversion.toType))
         ) {
-            if (conversion.fromType is ChoiceType && conversion.toType is ChoiceType) {
-                if (
-                    (conversion.fromType as ChoiceType).isSubSetOf(conversion.toType as ChoiceType)
-                ) {
-                    // conversion between compatible choice types requires no cast (i.e.
-                    // choice<Integer, String> can be
-                    // safely passed to choice<Integer, String, DateTime>
-                    return expression
-                }
-                // Otherwise, the choice is narrowing and a run-time As is required (to use only the
-                // expected target
-                // types)
+            // Otherwise, the choice is narrowing and a run-time As is required (to use only the
+            // expected target
+            // types)
+            if (
+                conversion.fromType is ChoiceType &&
+                    conversion.toType is ChoiceType &&
+                    (conversion.fromType).isSubSetOf(conversion.toType)
+            ) {
+                // conversion between compatible choice types requires no cast (i.e.
+                // choice<Integer, String> can be
+                // safely passed to choice<Integer, String, DateTime>
+                return expression
             }
             val castedOperand = buildAs(expression, conversion.toType)
             collapseTypeCase(castedOperand)
         } else
             @Suppress("ComplexCondition")
-            if (
+            when {
                 conversion.isCast &&
                     conversion.conversion != null &&
                     (conversion.fromType.isSuperTypeOf(conversion.conversion.fromType) ||
-                        conversion.fromType.isCompatibleWith(conversion.conversion.fromType))
-            ) {
-                val castedOperand = buildAs(expression, conversion.conversion.fromType)
-                var result = convertExpression(castedOperand, conversion.conversion)
-                if (conversion.hasAlternativeConversions()) {
-                    val caseResult = objectFactory.createCase()
-                    caseResult.resultType = result.resultType
-                    caseResult.caseItem.add(
-                        objectFactory
-                            .createCaseItem()
-                            .withWhen(buildIs(expression, conversion.conversion.fromType))
-                            .withThen(result)
-                    )
-                    for (alternative: Conversion in conversion.getAlternativeConversions()) {
+                        conversion.fromType.isCompatibleWith(conversion.conversion.fromType)) -> {
+                    val castedOperand = buildAs(expression, conversion.conversion.fromType)
+                    var result = convertExpression(castedOperand, conversion.conversion)
+                    if (conversion.hasAlternativeConversions()) {
+                        val caseResult = objectFactory.createCase()
+                        caseResult.resultType = result.resultType
                         caseResult.caseItem.add(
                             objectFactory
                                 .createCaseItem()
-                                .withWhen(buildIs(expression, alternative.fromType))
-                                .withThen(
-                                    convertExpression(
-                                        buildAs(expression, alternative.fromType),
-                                        alternative
-                                    )
-                                )
+                                .withWhen(buildIs(expression, conversion.conversion.fromType))
+                                .withThen(result)
                         )
+                        for (alternative: Conversion in conversion.getAlternativeConversions()) {
+                            caseResult.caseItem.add(
+                                objectFactory
+                                    .createCaseItem()
+                                    .withWhen(buildIs(expression, alternative.fromType))
+                                    .withThen(
+                                        convertExpression(
+                                            buildAs(expression, alternative.fromType),
+                                            alternative
+                                        )
+                                    )
+                            )
+                        }
+                        caseResult.withElse(buildNull(result.resultType))
+                        result = caseResult
                     }
-                    caseResult.withElse(buildNull(result.resultType))
-                    result = caseResult
+                    result
                 }
-                result
-            } else if (conversion.isListConversion) {
-                convertListExpression(expression, conversion)
-            } else if (conversion.isListDemotion) {
-                demoteListExpression(expression, conversion)
-            } else if (conversion.isListPromotion) {
-                promoteListExpression(expression, conversion)
-            } else if (conversion.isIntervalConversion) {
-                convertIntervalExpression(expression, conversion)
-            } else if (conversion.isIntervalDemotion) {
-                demoteIntervalExpression(expression, conversion)
-            } else if (conversion.isIntervalPromotion) {
-                promoteIntervalExpression(expression, conversion)
-            } else if (conversion.operator != null) {
-                val functionRef =
-                    objectFactory
-                        .createFunctionRef()
-                        .withLibraryName(conversion.operator.libraryName)
-                        .withName(conversion.operator.name)
-                        .withOperand(expression) as FunctionRef
-                val systemFunctionInvocation =
-                    systemFunctionResolver.resolveSystemFunction(functionRef)
-                if (systemFunctionInvocation != null) {
-                    return systemFunctionInvocation.expression
+                conversion.isListConversion -> {
+                    convertListExpression(expression, conversion)
                 }
-                resolveCall(
-                    functionRef.libraryName,
-                    functionRef.name!!,
-                    FunctionRefInvocation(functionRef),
-                    false,
-                    false
-                )
-                functionRef
-            } else {
-                when (conversion.toType) {
-                    resolveTypeName("System", "Boolean") -> {
-                        objectFactory
-                            .createToBoolean()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Integer") -> {
-                        objectFactory
-                            .createToInteger()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Long") -> {
-                        objectFactory
-                            .createToLong()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Decimal") -> {
-                        objectFactory
-                            .createToDecimal()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "String") -> {
-                        objectFactory
-                            .createToString()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Date") -> {
-                        objectFactory
-                            .createToDate()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "DateTime") -> {
-                        objectFactory
-                            .createToDateTime()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Time") -> {
-                        objectFactory
-                            .createToTime()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Quantity") -> {
-                        objectFactory
-                            .createToQuantity()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Ratio") -> {
-                        objectFactory
-                            .createToRatio()
-                            .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
-                    }
-                    resolveTypeName("System", "Concept") -> {
+                conversion.isListDemotion -> {
+                    demoteListExpression(expression, conversion)
+                }
+                conversion.isListPromotion -> {
+                    promoteListExpression(expression, conversion)
+                }
+                conversion.isIntervalConversion -> {
+                    convertIntervalExpression(expression, conversion)
+                }
+                conversion.isIntervalDemotion -> {
+                    demoteIntervalExpression(expression, conversion)
+                }
+                conversion.isIntervalPromotion -> {
+                    promoteIntervalExpression(expression, conversion)
+                }
+                conversion.operator != null -> {
+                    val functionRef =
                         objectFactory
-                            .createToConcept()
+                            .createFunctionRef()
+                            .withLibraryName(conversion.operator.libraryName)
+                            .withName(conversion.operator.name)
                             .withOperand(expression)
-                            .withResultType(conversion.toType) as Expression
+                    val systemFunctionInvocation =
+                        systemFunctionResolver.resolveSystemFunction(functionRef)
+                    if (systemFunctionInvocation != null) {
+                        return systemFunctionInvocation.expression
                     }
-                    else -> {
-                        val convertedOperand =
+                    resolveCall(
+                        functionRef.libraryName,
+                        functionRef.name!!,
+                        FunctionRefInvocation(functionRef),
+                        allowPromotionAndDemotion = false,
+                        allowFluent = false
+                    )
+                    functionRef
+                }
+                else -> {
+                    when (conversion.toType) {
+                        resolveTypeName("System", "Boolean") -> {
                             objectFactory
-                                .createConvert()
+                                .createToBoolean()
                                 .withOperand(expression)
-                                .withResultType(conversion.toType) as Convert
-                        if (convertedOperand.resultType is NamedType) {
-                            convertedOperand.toType = dataTypeToQName(convertedOperand.resultType)
-                        } else {
-                            convertedOperand.toTypeSpecifier =
-                                dataTypeToTypeSpecifier(convertedOperand.resultType)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Integer") -> {
+                            objectFactory
+                                .createToInteger()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Long") -> {
+                            objectFactory
+                                .createToLong()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Decimal") -> {
+                            objectFactory
+                                .createToDecimal()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "String") -> {
+                            objectFactory
+                                .createToString()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Date") -> {
+                            objectFactory
+                                .createToDate()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "DateTime") -> {
+                            objectFactory
+                                .createToDateTime()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Time") -> {
+                            objectFactory
+                                .createToTime()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Quantity") -> {
+                            objectFactory
+                                .createToQuantity()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Ratio") -> {
+                            objectFactory
+                                .createToRatio()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        resolveTypeName("System", "Concept") -> {
+                            objectFactory
+                                .createToConcept()
+                                .withOperand(expression)
+                                .withResultType(conversion.toType)
+                        }
+                        else -> {
+                            val convertedOperand =
+                                objectFactory
+                                    .createConvert()
+                                    .withOperand(expression)
+                                    .withResultType(conversion.toType)
+                            if (convertedOperand.resultType is NamedType) {
+                                convertedOperand.toType =
+                                    dataTypeToQName(convertedOperand.resultType)
+                            } else {
+                                convertedOperand.toTypeSpecifier =
+                                    dataTypeToTypeSpecifier(convertedOperand.resultType)
+                            }
+                            convertedOperand
                         }
-                        convertedOperand
                     }
                 }
             }
@@ -2200,7 +2176,13 @@ class LibraryBuilder(
         if (expectedType.isSuperTypeOf(actualType) || actualType.isCompatibleWith(expectedType)) {
             return
         }
-        val conversion = findConversion(actualType, expectedType, true, false)
+        val conversion =
+            findConversion(
+                actualType,
+                expectedType,
+                implicit = true,
+                allowPromotionAndDemotion = false
+            )
         if (conversion != null) {
             return
         }
@@ -2228,11 +2210,13 @@ class LibraryBuilder(
         // eliminate choices
         // based on convertibility
         if (!(first is ChoiceType || second is ChoiceType)) {
-            var conversion = findConversion(second, first, true, false)
+            var conversion =
+                findConversion(second, first, implicit = true, allowPromotionAndDemotion = false)
             if (conversion != null) {
                 return first
             }
-            conversion = findConversion(first, second, true, false)
+            conversion =
+                findConversion(first, second, implicit = true, allowPromotionAndDemotion = false)
             if (conversion != null) {
                 return second
             }
@@ -2254,7 +2238,7 @@ class LibraryBuilder(
         return first
     }
 
-    fun ensureCompatible(expression: Expression?, targetType: DataType?): Expression? {
+    fun ensureCompatible(expression: Expression?, targetType: DataType?): Expression {
         if (targetType == null) {
             return objectFactory.createNull()
         }
@@ -2263,7 +2247,7 @@ class LibraryBuilder(
         } else expression
     }
 
-    fun enforceCompatible(expression: Expression?, targetType: DataType?): Expression? {
+    fun enforceCompatible(expression: Expression?, targetType: DataType?): Expression {
         if (targetType == null) {
             return objectFactory.createNull()
         }
@@ -2272,7 +2256,7 @@ class LibraryBuilder(
         } else expression
     }
 
-    fun createLiteral(value: String?, type: String): Literal {
+    private fun createLiteral(value: String?, type: String): Literal {
         val resultType = resolveTypeName("System", type)
         val result =
             objectFactory
@@ -2322,7 +2306,7 @@ class LibraryBuilder(
         return result
     }
 
-    fun validateUnit(unit: String) {
+    private fun validateUnit(unit: String) {
         when (unit) {
             "year",
             "years",
@@ -2413,7 +2397,7 @@ class LibraryBuilder(
         return typeBuilder.dataTypeToQName(type)
     }
 
-    fun dataTypesToTypeSpecifiers(types: List<DataType>): List<TypeSpecifier> {
+    private fun dataTypesToTypeSpecifiers(types: List<DataType>): List<TypeSpecifier> {
         return typeBuilder.dataTypesToTypeSpecifiers(types)
     }
 
@@ -2451,133 +2435,110 @@ class LibraryBuilder(
     ): PropertyResolution? {
         var currentType: DataType? = sourceType
         while (currentType != null) {
-            if (currentType is ClassType) {
-                val classType: ClassType = currentType
-                if (identifier.startsWith("?") && isCompatibleWith("1.5")) {
-                    val searchPath: String = identifier.substring(1)
-                    for (s: SearchType in classType.getSearches()) {
-                        if ((s.name == searchPath)) {
-                            return PropertyResolution(s)
+            when {
+                currentType is ClassType -> {
+                    val classType: ClassType = currentType
+                    if (identifier.startsWith("?") && isCompatibleWith("1.5")) {
+                        val searchPath: String = identifier.substring(1)
+                        for (s: SearchType in classType.getSearches()) {
+                            if ((s.name == searchPath)) {
+                                return PropertyResolution(s)
+                            }
                         }
-                    }
-                } else {
-                    for (e: ClassTypeElement in classType.elements) {
-                        if ((e.name == identifier)) {
-                            if (e.prohibited) {
-                                throw IllegalArgumentException(
-                                    String.format(
-                                        Locale.US,
-                                        "Element %s cannot be referenced because it is marked prohibited in type %s.",
-                                        e.name,
-                                        currentType.name
-                                    )
-                                )
+                    } else {
+                        for (e: ClassTypeElement in classType.elements) {
+                            if ((e.name == identifier)) {
+                                require(!e.prohibited) {
+                                    "Element ${e.name} cannot be referenced because it is marked prohibited in type ${(currentType as ClassType).name}."
+                                }
+                                return PropertyResolution(e)
                             }
-                            return PropertyResolution(e)
                         }
                     }
                 }
-            } else if (currentType is TupleType) {
-                for (e: TupleTypeElement in currentType.elements) {
-                    if ((e.name == identifier)) {
-                        return PropertyResolution(e)
+                currentType is TupleType -> {
+                    for (e: TupleTypeElement in currentType.elements) {
+                        if ((e.name == identifier)) {
+                            return PropertyResolution(e)
+                        }
                     }
                 }
-            } else if (currentType is IntervalType) {
-                return when (identifier) {
-                    "low",
-                    "high" -> PropertyResolution(currentType.pointType, identifier)
-                    "lowClosed",
-                    "highClosed" ->
-                        PropertyResolution((resolveTypeName("System", "Boolean"))!!, identifier)
-                    else -> // ERROR:
-                    throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Invalid interval property name %s.",
-                                identifier
+                currentType is IntervalType -> {
+                    return when (identifier) {
+                        "low",
+                        "high" -> PropertyResolution(currentType.pointType, identifier)
+                        "lowClosed",
+                        "highClosed" ->
+                            PropertyResolution((resolveTypeName("System", "Boolean"))!!, identifier)
+                        else -> // ERROR:
+                        throw IllegalArgumentException(
+                                "Invalid interval property name $identifier."
                             )
-                        )
+                    }
                 }
-            } else if (currentType is ChoiceType) {
-                // TODO: Issue a warning if the property does not resolve against every type in the
-                // choice
-
-                // Resolve the property against each type in the choice
-                val resultTypes: MutableSet<DataType> = HashSet()
-                val resultTargetMaps: MutableMap<DataType, String> = HashMap()
-                var name: String? = null
-                for (choice: DataType in currentType.types) {
-                    val resolution: PropertyResolution? = resolveProperty(choice, identifier, false)
-                    if (resolution != null) {
-                        resultTypes.add(resolution.type)
-                        if (resolution.targetMap != null) {
-                            if (resultTargetMaps.containsKey(resolution.type)) {
-                                if (resultTargetMaps[resolution.type] != resolution.targetMap) {
-                                    throw IllegalArgumentException(
-                                        String.format(
-                                            Locale.US,
-                                            "Inconsistent target maps %s and %s for choice type %s",
-                                            resultTargetMaps[resolution.type],
-                                            resolution.targetMap,
-                                            resolution.type
-                                        )
-                                    )
+                currentType is ChoiceType -> {
+                    // TODO: Issue a warning if the property does not resolve against every type in
+                    // the
+                    // choice
+
+                    // Resolve the property against each type in the choice
+                    val resultTypes: MutableSet<DataType> = HashSet()
+                    val resultTargetMaps: MutableMap<DataType, String> = HashMap()
+                    var name: String? = null
+                    for (choice: DataType in currentType.types) {
+                        val resolution: PropertyResolution? =
+                            resolveProperty(choice, identifier, false)
+                        if (resolution != null) {
+                            resultTypes.add(resolution.type)
+                            if (resolution.targetMap != null) {
+                                if (resultTargetMaps.containsKey(resolution.type)) {
+                                    require(
+                                        resultTargetMaps[resolution.type] == resolution.targetMap
+                                    ) {
+                                        "Inconsistent target maps ${resultTargetMaps[resolution.type]} and ${resolution.targetMap} for choice type ${resolution.type}"
+                                    }
+                                } else {
+                                    resultTargetMaps[resolution.type] = resolution.targetMap
                                 }
-                            } else {
-                                resultTargetMaps[resolution.type] = resolution.targetMap
                             }
-                        }
-                        if (name == null) {
-                            name = resolution.name
-                        } else if (name != resolution.name) {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Inconsistent property resolution for choice type %s (was %s, is %s)",
-                                    choice.toString(),
-                                    name,
-                                    resolution.name
-                                )
-                            )
+                            if (name == null) {
+                                name = resolution.name
+                            } else
+                                require(name == resolution.name) {
+                                    "Inconsistent property resolution for choice type $choice (was $name, is ${resolution.name})"
+                                }
                         }
                     }
-                }
 
-                // The result type is a choice of all the resolved types
-                if (resultTypes.size > 1) {
-                    return PropertyResolution(ChoiceType(resultTypes), name!!, resultTargetMaps)
+                    // The result type is a choice of all the resolved types
+                    if (resultTypes.size > 1) {
+                        return PropertyResolution(ChoiceType(resultTypes), name!!, resultTargetMaps)
+                    }
+                    if (resultTypes.size == 1) {
+                        return PropertyResolution(
+                            resultTypes.iterator().next(),
+                            name!!,
+                            resultTargetMaps
+                        )
+                    }
                 }
-                if (resultTypes.size == 1) {
-                    return PropertyResolution(
-                        resultTypes.iterator().next(),
-                        name!!,
-                        resultTargetMaps
-                    )
+                currentType is ListType && listTraversal -> {
+                    // NOTE: FHIRPath path traversal support
+                    // Resolve property as a list of items of property of the element type
+                    val resolution: PropertyResolution? =
+                        resolveProperty(currentType.elementType, identifier)
+                    return PropertyResolution(ListType(resolution!!.type), (resolution.targetMap)!!)
                 }
-            } else if (currentType is ListType && listTraversal) {
-                // NOTE: FHIRPath path traversal support
-                // Resolve property as a list of items of property of the element type
-                val resolution: PropertyResolution? =
-                    resolveProperty(currentType.elementType, identifier)
-                return PropertyResolution(ListType(resolution!!.type), (resolution.targetMap)!!)
             }
-            if (currentType.baseType != null) {
+            if (currentType.baseType != DataType.ANY) {
                 currentType = currentType.baseType
             } else {
                 break
             }
         }
-        if (mustResolve) {
+        require(!mustResolve) {
             // ERROR:
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Member %s not found for type %s.",
-                    identifier,
-                    sourceType?.toLabel()
-                )
-            )
+            "Member $identifier not found for type ${sourceType?.toLabel()}."
         }
         return null
     }
@@ -2659,15 +2620,9 @@ class LibraryBuilder(
                 val expressionRef: ExpressionRef =
                     objectFactory.createExpressionRef().withName(element.name)
                 expressionRef.resultType = getExpressionDefResultType(element)
-                if (expressionRef.resultType == null) {
+                requireNotNull(expressionRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to expression %s because its definition contains errors.",
-                            expressionRef.name
-                        )
-                    )
+                    "Could not validate reference to expression ${expressionRef.name} because its definition contains errors."
                 }
                 return expressionRef
             }
@@ -2676,15 +2631,9 @@ class LibraryBuilder(
                 val parameterRef: ParameterRef =
                     objectFactory.createParameterRef().withName(element.name)
                 parameterRef.resultType = element.resultType
-                if (parameterRef.resultType == null) {
+                requireNotNull(parameterRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to parameter %s because its definition contains errors.",
-                            parameterRef.name
-                        )
-                    )
+                    "Could not validate reference to parameter ${parameterRef.name} because its definition contains errors."
                 }
                 return parameterRef
             }
@@ -2693,15 +2642,9 @@ class LibraryBuilder(
                 val valuesetRef: ValueSetRef =
                     objectFactory.createValueSetRef().withName(element.name)
                 valuesetRef.resultType = element.resultType
-                if (valuesetRef.resultType == null) {
+                requireNotNull(valuesetRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to valueset %s because its definition contains errors.",
-                            valuesetRef.name
-                        )
-                    )
+                    "Could not validate reference to valueset ${valuesetRef.name} because its definition contains errors."
                 }
                 if (isCompatibleWith("1.5")) {
                     valuesetRef.preserve = true
@@ -2713,15 +2656,9 @@ class LibraryBuilder(
                 val codesystemRef: CodeSystemRef =
                     objectFactory.createCodeSystemRef().withName(element.name)
                 codesystemRef.resultType = element.resultType
-                if (codesystemRef.resultType == null) {
+                requireNotNull(codesystemRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to codesystem %s because its definition contains errors.",
-                            codesystemRef.name
-                        )
-                    )
+                    "Could not validate reference to codesystem ${codesystemRef.name} because its definition contains errors."
                 }
                 return codesystemRef
             }
@@ -2729,15 +2666,9 @@ class LibraryBuilder(
                 checkLiteralContext()
                 val codeRef: CodeRef = objectFactory.createCodeRef().withName(element.name)
                 codeRef.resultType = element.resultType
-                if (codeRef.resultType == null) {
+                requireNotNull(codeRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to code %s because its definition contains errors.",
-                            codeRef.name
-                        )
-                    )
+                    "Could not validate reference to code ${codeRef.name} because its definition contains errors."
                 }
                 return codeRef
             }
@@ -2745,15 +2676,9 @@ class LibraryBuilder(
                 checkLiteralContext()
                 val conceptRef: ConceptRef = objectFactory.createConceptRef().withName(element.name)
                 conceptRef.resultType = element.resultType
-                if (conceptRef.resultType == null) {
+                requireNotNull(conceptRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to concept %s because its definition contains error.",
-                            conceptRef.name
-                        )
-                    )
+                    "Could not validate reference to concept ${conceptRef.name} because its definition contains error."
                 }
                 return conceptRef
             }
@@ -2787,12 +2712,7 @@ class LibraryBuilder(
             // ERROR:
             var message = resolvedIdentifierContext.warnCaseInsensitiveIfApplicable()
             if (message == null) {
-                message =
-                    String.format(
-                        Locale.US,
-                        "Could not resolve identifier %s in the current library.",
-                        identifier
-                    )
+                message = "Could not resolve identifier $identifier in the current library."
             }
 
             throw IllegalArgumentException(message)
@@ -2822,15 +2742,9 @@ class LibraryBuilder(
                 val parameterRef: ParameterRef =
                     objectFactory.createParameterRef().withName(contextParameter.name)
                 parameterRef.resultType = contextParameter.resultType
-                if (parameterRef.resultType == null) {
+                requireNotNull(parameterRef.resultType) {
                     // ERROR:
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not validate reference to parameter %s because its definition contains errors.",
-                            parameterRef.name
-                        )
-                    )
+                    "Could not validate reference to parameter ${parameterRef.name} because its definition contains errors."
                 }
                 return parameterRef
             }
@@ -2881,15 +2795,11 @@ class LibraryBuilder(
                 if (model.modelInfo.targetUrl != null) {
                     if (result != null) {
                         reportWarning(
-                            String.format(
-                                Locale.US,
-                                "Duplicate mapped model %s:%s%s",
-                                model.modelInfo.name,
-                                model.modelInfo.targetUrl,
+                            "Duplicate mapped model ${model.modelInfo.name}:${model.modelInfo.targetUrl}${
                                 if (model.modelInfo.targetVersion != null)
                                     "|" + model.modelInfo.targetVersion
                                 else ""
-                            ),
+                            }",
                             sourceContext
                         )
                     }
@@ -2968,86 +2878,82 @@ class LibraryBuilder(
         // If there is a trailing qualified path, the query is wrapped in a singletonFrom and a
         // property access
         // Any other target map results in an exception
-        if (targetMap.contains(";")) {
-            val typeCases: Array<String> =
-                targetMap.split(";".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
-            val c: Case = objectFactory.createCase()
-            for (typeCase: String in typeCases) {
-                if (typeCase.isNotEmpty()) {
-                    val splitIndex: Int = typeCase.indexOf(':')
-                    if (splitIndex <= 0) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Malformed type case in targetMap %s",
-                                targetMap
-                            )
-                        )
+        when {
+            targetMap.contains(";") -> {
+                val typeCases: Array<String> =
+                    targetMap.split(";".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
+                val c: Case = objectFactory.createCase()
+                for (typeCase: String in typeCases) {
+                    if (typeCase.isNotEmpty()) {
+                        val splitIndex: Int = typeCase.indexOf(':')
+                        require(splitIndex > 0) { "Malformed type case in targetMap $targetMap" }
+                        val typeCaseElement: String = typeCase.substring(0, splitIndex)
+                        val typeCaseType: DataType? = resolveTypeName(typeCaseElement)
+                        val typeCaseMap: String = typeCase.substring(splitIndex + 1)
+                        val ci: CaseItem =
+                            objectFactory
+                                .createCaseItem()
+                                .withWhen(
+                                    objectFactory
+                                        .createIs()
+                                        .withOperand(applyTargetMap(source, typeCaseMap))
+                                        .withIsType(dataTypeToQName(typeCaseType))
+                                )
+                                .withThen(applyTargetMap(source, typeCaseMap))
+                        ci.then!!.resultType = typeCaseType
+                        c.caseItem.add(ci)
                     }
-                    val typeCaseElement: String = typeCase.substring(0, splitIndex)
-                    val typeCaseType: DataType? = resolveTypeName(typeCaseElement)
-                    val typeCaseMap: String = typeCase.substring(splitIndex + 1)
-                    val ci: CaseItem =
-                        objectFactory
-                            .createCaseItem()
-                            .withWhen(
-                                objectFactory
-                                    .createIs()
-                                    .withOperand(applyTargetMap(source, typeCaseMap))
-                                    .withIsType(dataTypeToQName(typeCaseType))
-                            )
-                            .withThen(applyTargetMap(source, typeCaseMap))
-                    ci.then!!.resultType = typeCaseType
-                    c.caseItem.add(ci)
-                }
-            }
-            return when (c.caseItem.size) {
-                0 -> {
-                    buildNull(source!!.resultType)
                 }
-                1 -> {
-                    c.caseItem[0].then
-                }
-                else -> {
-                    c.`else` = (buildNull(source!!.resultType))
-                    c.resultType = source.resultType
-                    c
+                return when (c.caseItem.size) {
+                    0 -> {
+                        buildNull(source!!.resultType)
+                    }
+                    1 -> {
+                        c.caseItem[0].then
+                    }
+                    else -> {
+                        c.`else` = (buildNull(source!!.resultType))
+                        c.resultType = source.resultType
+                        c
+                    }
                 }
             }
-        } else if (targetMap.contains("(")) {
-            val invocationStart: Int = targetMap.indexOf("(")
-            val qualifiedFunctionName: String = targetMap.substring(0, invocationStart)
-            val nameParts: Array<String> =
-                qualifiedFunctionName
-                    .split("\\.".toRegex())
-                    .dropLastWhile { it.isEmpty() }
-                    .toTypedArray()
-            var libraryName: String? = null
-            var functionName: String? = qualifiedFunctionName
-            if (nameParts.size == 2) {
-                libraryName = nameParts[0]
-                functionName = nameParts[1]
-                ensureLibraryIncluded(libraryName, source)
-            }
-            val functionArgument: String =
-                targetMap.substring(invocationStart + 1, targetMap.lastIndexOf(')'))
-            val argumentSource: Expression? =
-                if ((functionArgument == "%value")) source
-                else applyTargetMap(source, functionArgument)
-
-            // NOTE: This is needed to work around the mapping for ToInterval
-            // FHIRHelpers defines multiple overloads of ToInterval, but the type mapping
-            // does not have the type of the source data type.
-            // All the mappings for ToInterval use FHIR.Period, so this is safe to assume
-            // In addition, no other FHIRHelpers functions use overloads (except ToString and
-            // ToDateTime,
-            // but those mappings expand the value element directly, rather than invoking the
-            // FHIRHelpers function)
-            var argumentSignature: TypeSpecifier? = null
-            if (options.signatureLevel != SignatureLevel.None) {
-                if (qualifiedFunctionName.equals("FHIRHelpers.ToInterval")) {
+            targetMap.contains("(") -> {
+                val invocationStart: Int = targetMap.indexOf("(")
+                val qualifiedFunctionName: String = targetMap.substring(0, invocationStart)
+                val nameParts: Array<String> =
+                    qualifiedFunctionName
+                        .split("\\.".toRegex())
+                        .dropLastWhile { it.isEmpty() }
+                        .toTypedArray()
+                var libraryName: String? = null
+                var functionName: String? = qualifiedFunctionName
+                if (nameParts.size == 2) {
+                    libraryName = nameParts[0]
+                    functionName = nameParts[1]
+                    ensureLibraryIncluded(libraryName, source)
+                }
+                val functionArgument: String =
+                    targetMap.substring(invocationStart + 1, targetMap.lastIndexOf(')'))
+                val argumentSource: Expression? =
+                    if ((functionArgument == "%value")) source
+                    else applyTargetMap(source, functionArgument)
+
+                // NOTE: This is needed to work around the mapping for ToInterval
+                // FHIRHelpers defines multiple overloads of ToInterval, but the type mapping
+                // does not have the type of the source data type.
+                // All the mappings for ToInterval use FHIR.Period, so this is safe to assume
+                // In addition, no other FHIRHelpers functions use overloads (except ToString and
+                // ToDateTime,
+                // but those mappings expand the value element directly, rather than invoking the
+                // FHIRHelpers function)
+                var argumentSignature: TypeSpecifier? = null
+                if (
+                    options.signatureLevel != SignatureLevel.None &&
+                        qualifiedFunctionName == "FHIRHelpers.ToInterval"
+                ) {
                     // Force loading of the FHIR model, as it's an implicit
-                    // dependency of the the target mapping here.
+                    // dependency of the target mapping here.
                     var fhirVersion = "4.0.1"
                     val qiCoreModel = this.getModel("QICore")
                     val version = qiCoreModel.modelInfo.version
@@ -3065,150 +2971,184 @@ class LibraryBuilder(
                             .withName(dataTypeToQName(resolveTypeName("FHIR", "Period")))
                     argumentSignature = namedTypeSpecifier
                 }
-            }
 
-            when (argumentSource!!.resultType) {
-                is ListType -> {
-                    val query: Query =
-                        objectFactory
-                            .createQuery()
-                            .withSource(
-                                objectFactory
-                                    .createAliasedQuerySource()
-                                    .withExpression(argumentSource)
-                                    .withAlias("\$this")
-                            )
-                    val fr: FunctionRef =
-                        objectFactory
-                            .createFunctionRef()
-                            .withLibraryName(libraryName)
-                            .withName(functionName)
-                            .withOperand(objectFactory.createAliasRef().withName("\$this"))
+                when (argumentSource!!.resultType) {
+                    is ListType -> {
+                        val query: Query =
+                            objectFactory
+                                .createQuery()
+                                .withSource(
+                                    objectFactory
+                                        .createAliasedQuerySource()
+                                        .withExpression(argumentSource)
+                                        .withAlias(FP_THIS)
+                                )
+                        val fr: FunctionRef =
+                            objectFactory
+                                .createFunctionRef()
+                                .withLibraryName(libraryName)
+                                .withName(functionName)
+                                .withOperand(objectFactory.createAliasRef().withName(FP_THIS))
 
-                    if (argumentSignature != null) {
-                        fr.signature.add(argumentSignature)
+                        if (argumentSignature != null) {
+                            fr.signature.add(argumentSignature)
+                        }
+
+                        // This doesn't quite work because the US.Core types aren't subtypes of FHIR
+                        // types.
+                        // resolveCall(libraryName, functionName, new FunctionRefInvocation(fr),
+                        // false,
+                        // false);
+                        query.`return` =
+                            (objectFactory
+                                .createReturnClause()
+                                .withDistinct(false)
+                                .withExpression(fr))
+                        query.resultType = source!!.resultType
+                        return query
                     }
+                    else -> {
+                        val fr: FunctionRef =
+                            objectFactory
+                                .createFunctionRef()
+                                .withLibraryName(libraryName)
+                                .withName(functionName)
+                                .withOperand(argumentSource)
+                        fr.resultType = source!!.resultType
 
-                    // This doesn't quite work because the US.Core types aren't subtypes of FHIR
-                    // types.
-                    // resolveCall(libraryName, functionName, new FunctionRefInvocation(fr), false,
-                    // false);
-                    query.`return` =
-                        (objectFactory.createReturnClause().withDistinct(false).withExpression(fr))
-                    query.resultType = source!!.resultType
-                    return query
-                }
-                else -> {
-                    val fr: FunctionRef =
-                        objectFactory
-                            .createFunctionRef()
-                            .withLibraryName(libraryName)
-                            .withName(functionName)
-                            .withOperand(argumentSource)
-                    fr.resultType = source!!.resultType
+                        if (argumentSignature != null) {
+                            fr.signature.add(argumentSignature)
+                        }
 
-                    if (argumentSignature != null) {
-                        fr.signature.add(argumentSignature)
+                        return fr
+                        // This doesn't quite work because the US.Core types aren't subtypes of FHIR
+                        // types,
+                        // or they are defined as System types and not FHIR types
+                        // return resolveCall(libraryName, functionName, new
+                        // FunctionRefInvocation(fr),
+                        // false, false);
                     }
-
-                    return fr
-                    // This doesn't quite work because the US.Core types aren't subtypes of FHIR
-                    // types,
-                    // or they are defined as System types and not FHIR types
-                    // return resolveCall(libraryName, functionName, new FunctionRefInvocation(fr),
-                    // false, false);
                 }
             }
-        } else if (targetMap.contains("[")) {
-            val indexerStart: Int = targetMap.indexOf("[")
-            val indexerEnd: Int = targetMap.indexOf("]")
-            val indexer: String = targetMap.substring(indexerStart + 1, indexerEnd)
-            val indexerPath: String = targetMap.substring(0, indexerStart)
-            var result: Expression? = null
-
-            // Apply sourcePaths to get to the indexer
-            val indexerPaths: Array<String> =
-                indexerPath.split("\\.".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
-            for (path: String in indexerPaths) {
-                if ((path == "%parent")) {
-                    if (source !is Property) {
-                        throw IllegalArgumentException(
-                            String.format(
-                                Locale.US,
-                                "Cannot expand target map %s for non-property-accessor type %s",
-                                targetMap,
-                                source!!.javaClass.simpleName
-                            )
-                        )
-                    }
-                    val sourceProperty: Property = source
-                    result =
-                        if (sourceProperty.source != null) {
+            targetMap.contains("[") -> {
+                val indexerStart: Int = targetMap.indexOf("[")
+                val indexerEnd: Int = targetMap.indexOf("]")
+                val indexer: String = targetMap.substring(indexerStart + 1, indexerEnd)
+                val indexerPath: String = targetMap.substring(0, indexerStart)
+                var result: Expression? = null
+
+                // Apply sourcePaths to get to the indexer
+                val indexerPaths: Array<String> =
+                    indexerPath.split("\\.".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
+                for (path: String in indexerPaths) {
+                    if ((path == "%parent")) {
+                        require(source is Property) {
+                            "Cannot expand target map $targetMap for non-property-accessor type ${source!!.javaClass.simpleName}"
+                        }
+                        val sourceProperty: Property = source
+                        result =
                             sourceProperty.source
-                        } else if (sourceProperty.scope != null) {
-                            resolveIdentifier(sourceProperty.scope!!, true)
-                        } else {
-                            throw IllegalArgumentException(
-                                String.format(
-                                    Locale.US,
-                                    "Cannot resolve %%parent reference in targetMap %s",
-                                    targetMap
-                                )
-                            )
+                                ?: sourceProperty.scope?.let {
+                                    resolveIdentifier(sourceProperty.scope!!, true)
+                                }
+                        requireNotNull(result) {
+                            "Cannot resolve %%parent reference in targetMap $targetMap"
                         }
-                } else {
-                    val p: Property =
-                        objectFactory.createProperty().withSource(result).withPath(path)
-                    result = p
+                    } else {
+                        val p: Property =
+                            objectFactory.createProperty().withSource(result).withPath(path)
+                        result = p
+                    }
                 }
-            }
 
-            // Build a query with the current result as source and the indexer content as criteria
-            // in the where clause
-            val querySource: AliasedQuerySource =
-                objectFactory.createAliasedQuerySource().withExpression(result).withAlias("\$this")
-            var criteria: Expression? = null
-            for (indexerItem: String in
-                indexer.split(",".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()) {
-                val indexerItems: Array<String> =
-                    indexerItem.split("=".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
-                if (indexerItems.size != 2) {
-                    throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Invalid indexer item %s in targetMap %s",
-                            indexerItem,
-                            targetMap
-                        )
-                    )
-                }
-                var left: Expression? = null
-                for (path: String in
-                    indexerItems[0]
-                        .split("\\.".toRegex())
-                        .dropLastWhile { it.isEmpty() }
-                        .toTypedArray()) {
-                    left =
-                        if (left == null) {
-                            objectFactory.createProperty().withScope("\$this").withPath(path)
-                        } else {
-                            objectFactory.createProperty().withSource(left).withPath(path)
+                // Build a query with the current result as source and the indexer content as
+                // criteria
+                // in the where clause
+                val querySource: AliasedQuerySource =
+                    objectFactory
+                        .createAliasedQuerySource()
+                        .withExpression(result)
+                        .withAlias(FP_THIS)
+                var criteria: Expression? = null
+                for (indexerItem: String in
+                    indexer.split(",".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()) {
+                    val indexerItems: Array<String> =
+                        indexerItem
+                            .split("=".toRegex())
+                            .dropLastWhile { it.isEmpty() }
+                            .toTypedArray()
+                    require(indexerItems.size == 2) {
+                        "Invalid indexer item $indexerItem in targetMap $targetMap"
+                    }
+                    var left: Expression? = null
+                    for (path: String in
+                        indexerItems[0]
+                            .split("\\.".toRegex())
+                            .dropLastWhile { it.isEmpty() }
+                            .toTypedArray()) {
+                        left =
+                            if (left == null) {
+                                objectFactory.createProperty().withScope(FP_THIS).withPath(path)
+                            } else {
+                                objectFactory.createProperty().withSource(left).withPath(path)
+                            }
+
+                        // HACK: Workaround the fact that we don't have type information for the
+                        // mapping
+                        // expansions...
+                        if ((path == "coding")) {
+                            left =
+                                objectFactory
+                                    .createFirst()
+                                    .withSource(left)
+                                    .withResultType(
+                                        this.getModel("FHIR").resolveTypeName("FHIR.coding")
+                                    )
                         }
+                        if ((path == "url")) {
+                            // HACK: This special cases FHIR model resolution
+                            left.resultType = this.getModel("FHIR").resolveTypeName("FHIR.uri")
+                            val ref: FunctionRef =
+                                objectFactory
+                                    .createFunctionRef()
+                                    .withLibraryName("FHIRHelpers")
+                                    .withName("ToString")
+                                    .withOperand(left)
+                            left =
+                                resolveCall(
+                                    ref.libraryName,
+                                    ref.name!!,
+                                    FunctionRefInvocation(ref),
+                                    allowPromotionAndDemotion = false,
+                                    allowFluent = false
+                                )
+                        }
+                    }
 
                     // HACK: Workaround the fact that we don't have type information for the mapping
                     // expansions...
-                    if ((path == "coding")) {
-                        left =
+                    // These hacks will be removed when addressed by the model info
+                    if ((indexerItems[0] == "code.coding.system")) {
+                        // HACK: This special cases FHIR model resolution
+                        left!!.resultType = this.getModel("FHIR").resolveTypeName("FHIR.uri")
+                        val ref: FunctionRef =
                             objectFactory
-                                .createFirst()
-                                .withSource(left)
-                                .withResultType(
-                                    this.getModel("FHIR").resolveTypeName("FHIR.coding")
-                                ) as Expression
+                                .createFunctionRef()
+                                .withLibraryName("FHIRHelpers")
+                                .withName("ToString")
+                                .withOperand(left)
+                        left =
+                            resolveCall(
+                                ref.libraryName,
+                                ref.name!!,
+                                FunctionRefInvocation(ref),
+                                allowPromotionAndDemotion = false,
+                                allowFluent = false
+                            )
                     }
-                    if ((path == "url")) {
+                    if ((indexerItems[0] == "code.coding.code")) {
                         // HACK: This special cases FHIR model resolution
-                        left.resultType = this.getModel("FHIR").resolveTypeName("FHIR.uri")
+                        left!!.resultType = this.getModel("FHIR").resolveTypeName("FHIR.code")
                         val ref: FunctionRef =
                             objectFactory
                                 .createFunctionRef()
@@ -3220,129 +3160,92 @@ class LibraryBuilder(
                                 ref.libraryName,
                                 ref.name!!,
                                 FunctionRefInvocation(ref),
-                                false,
-                                false
+                                allowPromotionAndDemotion = false,
+                                allowFluent = false
                             )
                     }
+                    val rightValue: String =
+                        indexerItems[1].substring(1, indexerItems[1].length - 1)
+                    val right: Expression =
+                        this.createLiteral(StringEscapeUtils.unescapeCql(rightValue))
+                    val criteriaItem: Expression =
+                        objectFactory.createEqual().withOperand(left!!, right)
+                    criteria =
+                        if (criteria == null) {
+                            criteriaItem
+                        } else {
+                            objectFactory.createAnd().withOperand(criteria, criteriaItem)
+                        }
                 }
+                val query: Query =
+                    objectFactory.createQuery().withSource(querySource).withWhere(criteria)
+                result = query
+                if (indexerEnd + 1 < targetMap.length) {
+                    // There are additional paths following the indexer, apply them
+                    var targetPath: String = targetMap.substring(indexerEnd + 1)
+                    if (targetPath.startsWith(".")) {
+                        targetPath = targetPath.substring(1)
+                    }
+                    if (targetPath.isNotEmpty()) {
+                        query.`return` =
+                            (objectFactory
+                                .createReturnClause()
+                                .withDistinct(false)
+                                .withExpression(
+                                    objectFactory
+                                        .createProperty()
+                                        .withSource(
+                                            objectFactory.createAliasRef().withName(FP_THIS)
+                                        )
+                                        .withPath(targetPath)
+                                ))
+                    }
 
-                // HACK: Workaround the fact that we don't have type information for the mapping
-                // expansions...
-                // These hacks will be removed when addressed by the model info
-                if ((indexerItems[0] == "code.coding.system")) {
-                    // HACK: This special cases FHIR model resolution
-                    left!!.resultType = this.getModel("FHIR").resolveTypeName("FHIR.uri")
-                    val ref: FunctionRef =
-                        objectFactory
-                            .createFunctionRef()
-                            .withLibraryName("FHIRHelpers")
-                            .withName("ToString")
-                            .withOperand(left) as FunctionRef
-                    left =
-                        resolveCall(
-                            ref.libraryName,
-                            ref.name!!,
-                            FunctionRefInvocation(ref),
-                            false,
-                            false
-                        )
+                    // The value reference should go inside the query, rather than being applied as
+                    // a
+                    // property outside of it
+                    // for (String path : targetPath.split("\\.")) {
+                    //    result = of.createProperty().withSource(result).withPath(path);
+                    // }
                 }
-                if ((indexerItems[0] == "code.coding.code")) {
-                    // HACK: This special cases FHIR model resolution
-                    left!!.resultType = this.getModel("FHIR").resolveTypeName("FHIR.code")
-                    val ref: FunctionRef =
-                        objectFactory
-                            .createFunctionRef()
-                            .withLibraryName("FHIRHelpers")
-                            .withName("ToString")
-                            .withOperand(left)
-                    left =
-                        resolveCall(
-                            ref.libraryName,
-                            ref.name!!,
-                            FunctionRefInvocation(ref),
-                            false,
-                            false
-                        )
+                if (source!!.resultType !is ListType) {
+                    // Use a singleton from since the source of the query is a list
+                    result = objectFactory.createSingletonFrom().withOperand(result)
                 }
-                val rightValue: String = indexerItems[1].substring(1, indexerItems[1].length - 1)
-                val right: Expression =
-                    this.createLiteral(StringEscapeUtils.unescapeCql(rightValue))
-                val criteriaItem: Expression =
-                    objectFactory.createEqual().withOperand(left!!, right)
-                criteria =
-                    if (criteria == null) {
-                        criteriaItem
-                    } else {
-                        objectFactory.createAnd().withOperand(criteria, criteriaItem)
-                    }
+                result.resultType = source.resultType
+                return result
             }
-            val query: Query =
-                objectFactory.createQuery().withSource(querySource).withWhere(criteria)
-            result = query
-            if (indexerEnd + 1 < targetMap.length) {
-                // There are additional paths following the indexer, apply them
-                var targetPath: String = targetMap.substring(indexerEnd + 1)
-                if (targetPath.startsWith(".")) {
-                    targetPath = targetPath.substring(1)
-                }
-                if (targetPath.isNotEmpty()) {
-                    query.`return` =
-                        (objectFactory
-                            .createReturnClause()
-                            .withDistinct(false)
-                            .withExpression(
-                                objectFactory
-                                    .createProperty()
-                                    .withSource(objectFactory.createAliasRef().withName("\$this"))
-                                    .withPath(targetPath)
-                            ))
+            targetMap.startsWith("%value.") -> {
+                val propertyName: String = targetMap.substring(@Suppress("MagicNumber") 7)
+                // If the source is a list, the mapping is expected to apply to every element in the
+                // list
+                // ((source $this return all $this.value)
+                if (source!!.resultType is ListType) {
+                    val s: AliasedQuerySource =
+                        objectFactory
+                            .createAliasedQuerySource()
+                            .withExpression(source)
+                            .withAlias(FP_THIS)
+                    val p: Property =
+                        objectFactory.createProperty().withScope(FP_THIS).withPath(propertyName)
+                    p.resultType = (source.resultType as ListType).elementType
+                    val r: ReturnClause =
+                        objectFactory.createReturnClause().withDistinct(false).withExpression(p)
+                    val q: Query = objectFactory.createQuery().withSource(s).withReturn(r)
+                    q.resultType = source.resultType
+                    return q
+                } else {
+                    val p: Property =
+                        objectFactory.createProperty().withSource(source).withPath(propertyName)
+                    p.resultType = source.resultType
+                    return p
                 }
-
-                // The value reference should go inside the query, rather than being applied as a
-                // property outside of it
-                // for (String path : targetPath.split("\\.")) {
-                //    result = of.createProperty().withSource(result).withPath(path);
-                // }
-            }
-            if (source!!.resultType !is ListType) {
-                // Use a singleton from since the source of the query is a list
-                result = objectFactory.createSingletonFrom().withOperand(result)
-            }
-            result.resultType = source.resultType
-            return result
-        } else if (targetMap.startsWith("%value.")) {
-            val propertyName: String = targetMap.substring(@Suppress("MagicNumber") 7)
-            // If the source is a list, the mapping is expected to apply to every element in the
-            // list
-            // ((source $this return all $this.value)
-            if (source!!.resultType is ListType) {
-                val s: AliasedQuerySource =
-                    objectFactory
-                        .createAliasedQuerySource()
-                        .withExpression(source)
-                        .withAlias("\$this")
-                val p: Property =
-                    objectFactory.createProperty().withScope("\$this").withPath(propertyName)
-                p.resultType = (source.resultType as ListType).elementType
-                val r: ReturnClause =
-                    objectFactory.createReturnClause().withDistinct(false).withExpression(p)
-                val q: Query = objectFactory.createQuery().withSource(s).withReturn(r)
-                q.resultType = source.resultType
-                return q
-            } else {
-                val p: Property =
-                    objectFactory.createProperty().withSource(source).withPath(propertyName)
-                p.resultType = source.resultType
-                return p
             }
         }
-        throw IllegalArgumentException(
-            String.format(Locale.US, "TargetMapping not implemented: %s", targetMap)
-        )
+        throw IllegalArgumentException("TargetMapping not implemented: $targetMap")
     }
 
-    @Suppress("LongMethod", "NestedBlockDepth")
+    @Suppress("LongMethod", "NestedBlockDepth", "CyclomaticComplexMethod")
     fun resolveAccessor(left: Expression, memberIdentifier: String): Expression? {
         // if left is a LibraryRef
         // if right is an identifier
@@ -3361,145 +3264,153 @@ class LibraryBuilder(
         // return a new Identifier with left as a qualifier
         // else
         // throws an error as an unresolved identifier
-        if (left is LibraryRef) {
-            val libraryName: String? = left.libraryName
-            val referencedLibrary: CompiledLibrary = resolveLibrary(libraryName)
-            val resolvedIdentifierContext: ResolvedIdentifierContext =
-                referencedLibrary.resolve(memberIdentifier)
-            val element = resolvedIdentifierContext.exactMatchElement
-            if (element != null) {
-                if (element is ExpressionDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: Expression =
-                        objectFactory
-                            .createExpressionRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = getExpressionDefResultType(element)
-                    return result
-                }
-                if (element is ParameterDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: Expression =
-                        objectFactory
-                            .createParameterRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = element.resultType
-                    return result
-                }
-                if (element is ValueSetDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: ValueSetRef =
-                        objectFactory
-                            .createValueSetRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = element.resultType
-                    if (isCompatibleWith("1.5")) {
-                        result.preserve = true
+        when {
+            left is LibraryRef -> {
+                val libraryName: String? = left.libraryName
+                val referencedLibrary: CompiledLibrary = resolveLibrary(libraryName)
+                val resolvedIdentifierContext: ResolvedIdentifierContext =
+                    referencedLibrary.resolve(memberIdentifier)
+                val element = resolvedIdentifierContext.exactMatchElement
+                if (element != null) {
+                    if (element is ExpressionDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: Expression =
+                            objectFactory
+                                .createExpressionRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = getExpressionDefResultType(element)
+                        return result
+                    }
+                    if (element is ParameterDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: Expression =
+                            objectFactory
+                                .createParameterRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = element.resultType
+                        return result
+                    }
+                    if (element is ValueSetDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: ValueSetRef =
+                            objectFactory
+                                .createValueSetRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = element.resultType
+                        if (isCompatibleWith("1.5")) {
+                            result.preserve = true
+                        }
+                        return result
+                    }
+                    if (element is CodeSystemDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: CodeSystemRef =
+                            objectFactory
+                                .createCodeSystemRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = element.resultType
+                        return result
+                    }
+                    if (element is CodeDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: CodeRef =
+                            objectFactory
+                                .createCodeRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = element.resultType
+                        return result
+                    }
+                    if (element is ConceptDef) {
+                        checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
+                        val result: ConceptRef =
+                            objectFactory
+                                .createConceptRef()
+                                .withLibraryName(libraryName)
+                                .withName(memberIdentifier)
+                        result.resultType = element.resultType
+                        return result
                     }
-                    return result
-                }
-                if (element is CodeSystemDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: CodeSystemRef =
-                        objectFactory
-                            .createCodeSystemRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = element.resultType
-                    return result
-                }
-                if (element is CodeDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: CodeRef =
-                        objectFactory
-                            .createCodeRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = element.resultType
-                    return result
-                }
-                if (element is ConceptDef) {
-                    checkAccessLevel(libraryName, memberIdentifier, element.accessLevel!!)
-                    val result: ConceptRef =
-                        objectFactory
-                            .createConceptRef()
-                            .withLibraryName(libraryName)
-                            .withName(memberIdentifier)
-                    result.resultType = element.resultType
-                    return result
                 }
-            }
 
-            // ERROR:
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Could not resolve identifier %s in library %s.",
-                    memberIdentifier,
-                    referencedLibrary.identifier!!.id
-                )
-            )
-        } else if (left is AliasRef) {
-            val resolution: PropertyResolution? = resolveProperty(left.resultType, memberIdentifier)
-            val result: Expression =
-                buildProperty(left.name, resolution!!.name, resolution.isSearch, resolution.type)
-            return applyTargetMap(result, resolution.targetMap)
-        } else if (left.resultType is ListType && listTraversal) {
-            // NOTE: FHIRPath path traversal support
-            // Resolve property access of a list of items as a query:
-            // listValue.property ::= listValue X where X.property is not null return all X.property
-            val listType: ListType = left.resultType as ListType
-            val resolution: PropertyResolution? =
-                resolveProperty(listType.elementType, memberIdentifier)
-            var accessor: Expression? =
-                buildProperty(
-                    objectFactory.createAliasRef().withName("\$this"),
-                    resolution!!.name,
-                    resolution.isSearch,
-                    resolution.type
-                )
-            accessor = applyTargetMap(accessor, resolution.targetMap)
-            val not: Expression = buildIsNotNull(accessor)
-
-            // Recreate property, it needs to be accessed twice
-            accessor =
-                buildProperty(
-                    objectFactory.createAliasRef().withName("\$this"),
-                    resolution.name,
-                    resolution.isSearch,
-                    resolution.type
+                // ERROR:
+                throw IllegalArgumentException(
+                    "Could not resolve identifier $memberIdentifier in library ${referencedLibrary.identifier!!.id}."
                 )
-            accessor = applyTargetMap(accessor, resolution.targetMap)
-            val source: AliasedQuerySource =
-                objectFactory.createAliasedQuerySource().withExpression(left).withAlias("\$this")
-            source.resultType = left.resultType
-            val query: Query =
-                objectFactory
-                    .createQuery()
-                    .withSource(source)
-                    .withWhere(not)
-                    .withReturn(
-                        objectFactory
-                            .createReturnClause()
-                            .withDistinct(false)
-                            .withExpression(accessor)
+            }
+            left is AliasRef -> {
+                val resolution: PropertyResolution? =
+                    resolveProperty(left.resultType, memberIdentifier)
+                val result: Expression =
+                    buildProperty(
+                        left.name,
+                        resolution!!.name,
+                        resolution.isSearch,
+                        resolution.type
+                    )
+                return applyTargetMap(result, resolution.targetMap)
+            }
+            left.resultType is ListType && listTraversal -> {
+                // NOTE: FHIRPath path traversal support
+                // Resolve property access of a list of items as a query:
+                // listValue.property ::= listValue X where X.property is not null return all
+                // X.property
+                val listType: ListType = left.resultType as ListType
+                val resolution: PropertyResolution? =
+                    resolveProperty(listType.elementType, memberIdentifier)
+                var accessor: Expression? =
+                    buildProperty(
+                        objectFactory.createAliasRef().withName(FP_THIS),
+                        resolution!!.name,
+                        resolution.isSearch,
+                        resolution.type
+                    )
+                accessor = applyTargetMap(accessor, resolution.targetMap)
+                val not: Expression = buildIsNotNull(accessor)
+
+                // Recreate property, it needs to be accessed twice
+                accessor =
+                    buildProperty(
+                        objectFactory.createAliasRef().withName(FP_THIS),
+                        resolution.name,
+                        resolution.isSearch,
+                        resolution.type
                     )
-            query.resultType = ListType(accessor!!.resultType!!)
-            if (accessor.resultType is ListType) {
-                val result: Flatten = objectFactory.createFlatten().withOperand(query)
-                result.resultType = accessor.resultType
+                accessor = applyTargetMap(accessor, resolution.targetMap)
+                val source: AliasedQuerySource =
+                    objectFactory.createAliasedQuerySource().withExpression(left).withAlias(FP_THIS)
+                source.resultType = left.resultType
+                val query: Query =
+                    objectFactory
+                        .createQuery()
+                        .withSource(source)
+                        .withWhere(not)
+                        .withReturn(
+                            objectFactory
+                                .createReturnClause()
+                                .withDistinct(false)
+                                .withExpression(accessor)
+                        )
+                query.resultType = ListType(accessor!!.resultType!!)
+                if (accessor.resultType is ListType) {
+                    val result: Flatten = objectFactory.createFlatten().withOperand(query)
+                    result.resultType = accessor.resultType
+                    return result
+                }
+                return query
+            }
+            else -> {
+                val resolution: PropertyResolution? =
+                    resolveProperty(left.resultType, memberIdentifier)
+                var result: Expression? =
+                    buildProperty(left, resolution!!.name, resolution.isSearch, resolution.type)
+                result = applyTargetMap(result, resolution.targetMap)
                 return result
             }
-            return query
-        } else {
-            val resolution: PropertyResolution? = resolveProperty(left.resultType, memberIdentifier)
-            var result: Expression? =
-                buildProperty(left, resolution!!.name, resolution.isSearch, resolution.type)
-            result = applyTargetMap(result, resolution.targetMap)
-            return result
         }
     }
 
@@ -3507,7 +3418,7 @@ class LibraryBuilder(
         if (inQueryContext()) {
             val query = peekQueryContext()
             if (query.inSortClause() && !query.isSingular) {
-                if (identifier == "\$this") {
+                if (identifier == FP_THIS) {
                     val result = objectFactory.createIdentifierRef().withName(identifier)
                     result.resultType = query.resultElementType
                     return result
@@ -3541,9 +3452,9 @@ class LibraryBuilder(
         if (inQueryContext()) {
             val query = peekQueryContext()
             if (query.isImplicit) {
-                val source = resolveAlias("\$this")
+                val source = resolveAlias(FP_THIS)
                 if (source != null) {
-                    val aliasRef = objectFactory.createAliasRef().withName("\$this")
+                    val aliasRef = objectFactory.createAliasRef().withName(FP_THIS)
                     if (source.resultType is ListType) {
                         aliasRef.resultType = (source.resultType as ListType).elementType
                     } else {
@@ -3579,7 +3490,7 @@ class LibraryBuilder(
                     return objectFactory
                         .createOperandRef()
                         .withName(identifier)
-                        .withResultType(operand.resultType) as OperandRef
+                        .withResultType(operand.resultType)
                 }
             }
         }
@@ -3620,12 +3531,7 @@ class LibraryBuilder(
             }
         }
         throw IllegalArgumentException(
-            String.format(
-                Locale.US,
-                "Invalid context reference from %s context to %s context.",
-                currentExpressionContext(),
-                expressionDef.context
-            )
+            "Invalid context reference from ${currentExpressionContext()} context to ${expressionDef.context} context."
         )
     }
 
@@ -3633,26 +3539,7 @@ class LibraryBuilder(
         GLOBAL,
         LOCAL
     }
-    /**
-     * Add an identifier to the deque to indicate that we are considering it for consideration for
-     * identifier hiding and adding a compiler warning if this is the case.
-     *
-     * For example, if an alias within an expression body has the same name as a parameter,
-     * execution would have added the parameter identifier and the next execution would consider an
-     * alias with the same name, thus resulting in a warning.
-     *
-     * Exact case matching as well as case-insensitive matching are considered. If known, the type
-     * of the structure in question will be considered in crafting the warning message, as per the
-     * [Element] parameter.
-     *
-     * Also, special case function overloads so that only a single overloaded function name is taken
-     * into account.
-     *
-     * @param identifier The identifier belonging to the parameter, expression, function, alias,
-     *   etc, to be evaluated.
-     * @param trackable The construct trackable, for example [ExpressionRef].
-     * @param scope the scope of the current identifier
-     */
+
     /**
      * Add an identifier to the deque to indicate that we are considering it for consideration for
      * identifier hiding and adding a compiler warning if this is the case.
@@ -3671,7 +3558,7 @@ class LibraryBuilder(
      * Default scope is [IdentifierScope.LOCAL]
      *
      * @param identifier The identifier belonging to the parameter, expression, function, alias,
-     *   etc, to be evaluated.
+     *   etc., to be evaluated.
      * @param element The construct trackable, for example [ExpressionRef].
      */
     @JvmOverloads
@@ -3681,7 +3568,7 @@ class LibraryBuilder(
         scope: IdentifierScope = IdentifierScope.LOCAL
     ) {
         val localMatch =
-            if (!localIdentifierStack.isEmpty())
+            if (localIdentifierStack.isNotEmpty())
                 findMatchingIdentifierContext(localIdentifierStack.peek(), identifier)
             else Optional.empty()
         val globalMatch = findMatchingIdentifierContext(globalIdentifiers, identifier)
@@ -3740,8 +3627,6 @@ class LibraryBuilder(
         localIdentifierStack.pop()
     }
 
-    // TODO:  consider other structures that should only trigger a readonly check of identifier
-    // hiding
     private fun shouldAddIdentifierContext(element: Element?): Boolean {
         return element !is Literal
     }
@@ -3753,19 +3638,9 @@ class LibraryBuilder(
     ): String {
         val elementString = lookupElementWarning(element)
         return if (element is Literal) {
-            String.format(
-                Locale.US,
-                "You used a string literal: [%s] here that matches an identifier in scope: [%s]. Did you mean to use the identifier instead?",
-                identifierParam,
-                matchedIdentifier
-            )
+            "You used a string literal: [$identifierParam] here that matches an identifier in scope: [$matchedIdentifier]. Did you mean to use the identifier instead?"
         } else
-            String.format(
-                Locale.US,
-                "%s identifier [%s] is hiding another identifier of the same name.",
-                elementString,
-                identifierParam
-            )
+            "$elementString identifier [$identifierParam] is hiding another identifier of the same name."
     }
 
     private inner class Scope {
@@ -3790,7 +3665,7 @@ class LibraryBuilder(
     }
 
     fun determineRootCause(): Exception? {
-        if (!expressionDefinitions.isEmpty()) {
+        if (expressionDefinitions.isNotEmpty()) {
             val currentContext = expressionDefinitions.peek()
             if (currentContext != null) {
                 return currentContext.rootCause
@@ -3800,22 +3675,16 @@ class LibraryBuilder(
     }
 
     fun setRootCause(rootCause: Exception?) {
-        if (!expressionDefinitions.isEmpty()) {
+        if (expressionDefinitions.isNotEmpty()) {
             val currentContext = expressionDefinitions.peek()
             currentContext?.rootCause = rootCause
         }
     }
 
     fun pushExpressionDefinition(identifier: String) {
-        if (expressionDefinitions.contains(identifier)) {
+        require(!expressionDefinitions.contains(identifier)) {
             // ERROR:
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Cannot resolve reference to expression or function %s because it results in a circular reference.",
-                    identifier
-                )
-            )
+            "Cannot resolve reference to expression or function $identifier because it results in a circular reference."
         }
         expressionDefinitions.push(ExpressionDefinitionContext(identifier))
     }
@@ -3841,22 +3710,22 @@ class LibraryBuilder(
         expressionContext.pop()
     }
 
-    fun currentExpressionContext(): String {
+    private fun currentExpressionContext(): String {
         check(!expressionContext.empty()) { "Expression context stack is empty." }
         return expressionContext.peek()
     }
 
-    fun inSpecificContext(): Boolean {
+    private fun inSpecificContext(): Boolean {
         return !inUnfilteredContext()
     }
 
-    fun inUnfilteredContext(): Boolean {
+    private fun inUnfilteredContext(): Boolean {
         return currentExpressionContext() == "Unfiltered" ||
             isCompatibilityLevel3 && currentExpressionContext() == "Population"
     }
 
-    fun inQueryContext(): Boolean {
-        return hasScope() && scope.queries.size > 0
+    private fun inQueryContext(): Boolean {
+        return hasScope() && scope.queries.isNotEmpty()
     }
 
     fun pushQueryContext(context: QueryContext) {
@@ -3880,7 +3749,7 @@ class LibraryBuilder(
     }
 
     fun hasExpressionTarget(): Boolean {
-        return hasScope() && !scope.targets.isEmpty()
+        return hasScope() && scope.targets.isNotEmpty()
     }
 
     fun beginFunctionDef(functionDef: FunctionDef) {
@@ -3900,7 +3769,7 @@ class LibraryBuilder(
         literalContext--
     }
 
-    fun inLiteralContext(): Boolean {
+    private fun inLiteralContext(): Boolean {
         return literalContext > 0
     }
 
@@ -3919,52 +3788,27 @@ class LibraryBuilder(
         typeSpecifierContext--
     }
 
-    fun inTypeSpecifierContext(): Boolean {
+    private fun inTypeSpecifierContext(): Boolean {
         return typeSpecifierContext > 0
     }
 
     companion object {
         private fun lookupElementWarning(element: Any?): String {
-            // TODO:  this list is not exhaustive and may need to be updated
-            when (element) {
-                is ExpressionDef -> {
-                    return "An expression"
-                }
-                is ParameterDef -> {
-                    return "A parameter"
-                }
-                is ValueSetDef -> {
-                    return "A valueset"
-                }
-                is CodeSystemDef -> {
-                    return "A codesystem"
-                }
-                is CodeDef -> {
-                    return "A code"
-                }
-                is ConceptDef -> {
-                    return "A concept"
-                }
-                is IncludeDef -> {
-                    return "An include"
-                }
-                is AliasedQuerySource -> {
-                    return "An alias"
-                }
-                is LetClause -> {
-                    return "A let"
-                }
-                is OperandDef -> {
-                    return "An operand"
-                }
-                is UsingDef -> {
-                    return "A using"
-                }
-                is Literal -> {
-                    return "A literal"
-                }
+            return when (element) {
+                is ExpressionDef -> "An expression"
+                is ParameterDef -> "A parameter"
+                is ValueSetDef -> "A valueset"
+                is CodeSystemDef -> "A codesystem"
+                is CodeDef -> "A code"
+                is ConceptDef -> "A concept"
+                is IncludeDef -> "An include"
+                is AliasedQuerySource -> "An alias"
+                is LetClause -> "A let"
+                is OperandDef -> "An operand"
+                is UsingDef -> "A using"
+                is Literal -> "A literal"
                 // default message if no match is made:
-                else -> return "An [unknown structure]"
+                else -> "An [unknown structure]"
             }
         }
     }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryManager.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryManager.kt
index 90153e9f4..9a08003d8 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryManager.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryManager.kt
@@ -3,7 +3,6 @@
 package org.cqframework.cql.cql2elm
 
 import java.io.*
-import java.util.*
 import kotlin.collections.ArrayList
 import kotlin.collections.HashMap
 import kotlin.collections.HashSet
@@ -44,9 +43,6 @@ constructor(
      * namespace in a namespace-aware context
      */
     fun isWellKnownLibraryName(unqualifiedIdentifier: String?): Boolean {
-        if (unqualifiedIdentifier == null) {
-            return false
-        }
         return when (unqualifiedIdentifier) {
             "FHIRHelpers" -> true
             else -> false
@@ -54,24 +50,24 @@ constructor(
     }
 
     fun resolveLibrary(
-        libraryIdentifier: VersionedIdentifier?,
+        libraryIdentifier: VersionedIdentifier,
         cacheMode: CacheMode
     ): CompiledLibrary {
         return this.resolveLibrary(libraryIdentifier, ArrayList(), cacheMode)
     }
 
-    fun canResolveLibrary(libraryIdentifier: VersionedIdentifier?): Boolean {
-        val lib = this.resolveLibrary(libraryIdentifier)
-        return lib != null
+    fun canResolveLibrary(libraryIdentifier: VersionedIdentifier): Boolean {
+        // This throws an exception if the library cannot be resolved
+        this.resolveLibrary(libraryIdentifier)
+        return true
     }
 
     @JvmOverloads
     fun resolveLibrary(
-        libraryIdentifier: VersionedIdentifier?,
+        libraryIdentifier: VersionedIdentifier,
         errors: MutableList<CqlCompilerException> = ArrayList(),
         cacheMode: CacheMode = CacheMode.READ_WRITE
     ): CompiledLibrary {
-        require(libraryIdentifier != null) { "libraryIdentifier is null." }
         require(!libraryIdentifier.id.isNullOrEmpty()) { "libraryIdentifier Id is null." }
         var library: CompiledLibrary?
         if (cacheMode != CacheMode.NONE) {
@@ -106,12 +102,8 @@ constructor(
             val cqlSource: InputStream =
                 librarySourceLoader.getLibrarySource(libraryIdentifier)
                     ?: throw CqlIncludeException(
-                        String.format(
-                            Locale.US,
-                            "Could not load source for library %s, version %s.",
-                            libraryIdentifier.id,
-                            libraryIdentifier.version
-                        ),
+                        """Could not load source for library ${libraryIdentifier.id},
+                                 version ${libraryIdentifier.version}.""",
                         libraryIdentifier.system,
                         libraryIdentifier.id!!,
                         libraryIdentifier.version
@@ -130,13 +122,8 @@ constructor(
                     libraryIdentifier.version != result!!.identifier!!.version)
             ) {
                 throw CqlIncludeException(
-                    String.format(
-                        Locale.US,
-                        "Library %s was included as version %s, but version %s of the library was found.",
-                        libraryPath,
-                        libraryIdentifier.version,
-                        result.identifier!!.version
-                    ),
+                    """Library $libraryPath was included as version ${libraryIdentifier.version}, 
+                        but version ${result.identifier!!.version} of the library was found.""",
                     libraryIdentifier.system,
                     libraryIdentifier.id!!,
                     libraryIdentifier.version
@@ -144,12 +131,7 @@ constructor(
             }
         } catch (e: IOException) {
             throw CqlIncludeException(
-                String.format(
-                    Locale.US,
-                    "Errors occurred translating library %s, version %s.",
-                    libraryPath,
-                    libraryIdentifier.version
-                ),
+                "Errors occurred translating library $libraryPath, version ${libraryIdentifier.version}.",
                 libraryIdentifier.system!!,
                 libraryIdentifier.id!!,
                 libraryIdentifier.version,
@@ -158,15 +140,10 @@ constructor(
         }
         if (result == null) {
             throw CqlIncludeException(
-                String.format(
-                    Locale.US,
-                    "Could not load source for library %s, version %s.",
-                    libraryPath,
-                    libraryIdentifier.version
-                ),
+                "Could not load source for library $libraryPath.",
                 libraryIdentifier.system,
                 libraryIdentifier.id!!,
-                libraryIdentifier.version
+                null
             )
         } else {
             sortStatements(result)
@@ -328,8 +305,8 @@ constructor(
     }
 
     @Suppress("NestedBlockDepth")
-    fun hasSignature(library: Library?): Boolean {
-        if (library?.statements != null) {
+    private fun hasSignature(library: Library): Boolean {
+        if (library.statements != null) {
             // Just a quick top-level scan for signatures. To fully verify we'd have to
             // recurse all
             // the way down. At that point, let's just translate.
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryReaderUtil.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryReaderUtil.kt
deleted file mode 100644
index 46ebd90be..000000000
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibraryReaderUtil.kt
+++ /dev/null
@@ -1,53 +0,0 @@
-@file:Suppress("WildcardImport")
-
-package org.cqframework.cql.cql2elm
-
-import java.io.*
-import java.net.URI
-import java.net.URISyntaxException
-import java.net.URL
-import java.util.*
-import javax.xml.transform.Source
-import javax.xml.transform.stream.StreamSource
-
-object LibraryReaderUtil {
-    /** Creates [Source] from various JSON representation. */
-    @Suppress("ReturnCount")
-    @Throws(IOException::class)
-    fun toSource(json: Any?): Source {
-        var json: Any? = json ?: throw CqlCompilerException("no JSON is given")
-        if (json is String) {
-            json =
-                try {
-                    URI(json)
-                } catch (@Suppress("SwallowedException") e: URISyntaxException) {
-                    File(json)
-                }
-        }
-        if (json is File) {
-            return StreamSource(json as File?)
-        }
-        if (json is URI) {
-            json = json.toURL()
-        }
-        if (json is URL) {
-            return StreamSource(json.toExternalForm())
-        }
-        if (json is InputStream) {
-            return StreamSource(json as InputStream?)
-        }
-        if (json is Reader) {
-            return StreamSource(json as Reader?)
-        }
-        if (json is Source) {
-            return json
-        }
-        throw CqlCompilerException(
-            String.format(
-                Locale.US,
-                "Could not determine access path for input of type %s.",
-                json!!.javaClass
-            )
-        )
-    }
-}
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibrarySourceLoader.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibrarySourceLoader.kt
index 213b2a92a..19abe867e 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibrarySourceLoader.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/LibrarySourceLoader.kt
@@ -20,14 +20,4 @@ interface LibrarySourceLoader {
         }
         return null
     }
-
-    fun isLibraryContentAvailable(
-        libraryIdentifier: VersionedIdentifier,
-        type: LibraryContentType
-    ): Boolean {
-        if (LibraryContentType.CQL == type) {
-            return getLibrarySource(libraryIdentifier) != null
-        }
-        return false
-    }
 }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelInfoLoader.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelInfoLoader.kt
index 63f37a096..0488ee54e 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelInfoLoader.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelInfoLoader.kt
@@ -1,7 +1,6 @@
 package org.cqframework.cql.cql2elm
 
 import java.nio.file.Path
-import java.util.*
 import kotlin.collections.ArrayList
 import org.hl7.cql.model.ModelIdentifier
 import org.hl7.cql.model.ModelInfoProvider
@@ -36,13 +35,10 @@ class ModelInfoLoader : NamespaceAware, PathAware {
             }
         }
         requireNotNull(modelInfo) {
-            String.format(
-                Locale.US,
-                "Could not resolve model info provider for model %s, version %s.",
+            "Could not resolve model info provider for model ${
                 if (modelIdentifier.system == null) modelIdentifier.id
-                else NamespaceManager.getPath(modelIdentifier.system, modelIdentifier.id),
-                modelIdentifier.version
-            )
+                else NamespaceManager.getPath(modelIdentifier.system, modelIdentifier.id)
+            }, version ${modelIdentifier.version}."
         }
         return modelInfo
     }
@@ -82,9 +78,7 @@ class ModelInfoLoader : NamespaceAware, PathAware {
     }
 
     override fun setPath(path: Path) {
-        require(path.toFile().isDirectory) {
-            String.format(Locale.US, "path '%s' is not a valid directory", path)
-        }
+        require(path.toFile().isDirectory) { "path '$path' is not a valid directory" }
         this.path = path
         for (provider in getProviders()) {
             if (provider is PathAware) {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelManager.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelManager.kt
index 710c346a2..608baaa16 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelManager.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/ModelManager.kt
@@ -16,12 +16,18 @@ class ModelManager {
     var modelInfoLoader: ModelInfoLoader? = null
         private set
 
-    private val models: MutableMap<String, Model?> = HashMap()
+    private val models: MutableMap<String, Model> = HashMap()
     private val loadingModels: MutableSet<String> = HashSet()
-    private val modelsByUri: MutableMap<String, Model?> = HashMap()
-    private val globalCache: MutableMap<ModelIdentifier, Model?>
-    var isDefaultModelInfoLoadingEnabled = true
-        private set
+    private val modelsByUri: MutableMap<String, Model> = HashMap()
+
+    /**
+     * The global cache is by @{org.hl7.cql.model.ModelIdentifier}, while the local cache is by
+     * name. This is because the translator expects the ModelManager to only permit loading of a
+     * single version of a given Model in a single translation context, while the global cache is
+     * for all versions of Models
+     */
+    private val globalCache: MutableMap<ModelIdentifier, Model>
+    private var isDefaultModelInfoLoadingEnabled = true
 
     constructor() {
         namespaceManager = NamespaceManager()
@@ -30,7 +36,7 @@ class ModelManager {
     }
 
     /** @param globalCache cache for Models by ModelIdentifier. Expected to be thread-safe. */
-    constructor(globalCache: MutableMap<ModelIdentifier, Model?>) {
+    constructor(globalCache: MutableMap<ModelIdentifier, Model>) {
         namespaceManager = NamespaceManager()
         this.globalCache = globalCache
         initialize()
@@ -43,7 +49,7 @@ class ModelManager {
         initialize()
     }
 
-    constructor(path: Path?, globalCache: MutableMap<ModelIdentifier, Model?>) {
+    constructor(path: Path?, globalCache: MutableMap<ModelIdentifier, Model>) {
         namespaceManager = NamespaceManager()
         this.globalCache = globalCache
         this.path = path
@@ -59,7 +65,7 @@ class ModelManager {
 
     constructor(
         enableDefaultModelInfoLoading: Boolean,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         namespaceManager = NamespaceManager()
         this.globalCache = globalCache
@@ -78,7 +84,7 @@ class ModelManager {
     constructor(
         enableDefaultModelInfoLoading: Boolean,
         path: Path?,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         namespaceManager = NamespaceManager()
         this.globalCache = globalCache
@@ -95,7 +101,7 @@ class ModelManager {
 
     constructor(
         namespaceManager: NamespaceManager,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         this.namespaceManager = namespaceManager
         this.globalCache = globalCache
@@ -112,7 +118,7 @@ class ModelManager {
     constructor(
         namespaceManager: NamespaceManager,
         path: Path?,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         this.namespaceManager = namespaceManager
         this.globalCache = globalCache
@@ -130,7 +136,7 @@ class ModelManager {
     constructor(
         namespaceManager: NamespaceManager,
         enableDefaultModelInfoLoading: Boolean,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         this.namespaceManager = namespaceManager
         this.globalCache = globalCache
@@ -154,7 +160,7 @@ class ModelManager {
         namespaceManager: NamespaceManager,
         enableDefaultModelInfoLoading: Boolean,
         path: Path?,
-        globalCache: MutableMap<ModelIdentifier, Model?>
+        globalCache: MutableMap<ModelIdentifier, Model>
     ) {
         this.namespaceManager = namespaceManager
         this.globalCache = globalCache
@@ -171,16 +177,6 @@ class ModelManager {
         }
     }
 
-    /**
-     * The global cache is by @{org.hl7.cql.model.ModelIdentifier}, while the local cache is by
-     * name. This is because the translator expects the ModelManager to only permit loading of a
-     * single version of a given Model in a single translation context, while the global cache is
-     * for all versions of Models
-     */
-    fun getGlobalCache(): Map<ModelIdentifier, Model?> {
-        return globalCache
-    }
-
     /*
     A "well-known" model name is one that is allowed to resolve without a namespace in a namespace-aware context
      */
@@ -218,9 +214,7 @@ class ModelManager {
     }
 
     private fun pushLoading(modelId: String) {
-        require(!loadingModels.contains(modelId)) {
-            String.format(Locale.US, "Circular model reference %s", modelId)
-        }
+        require(!loadingModels.contains(modelId)) { "Circular model reference $modelId" }
         loadingModels.add(modelId)
     }
 
@@ -245,16 +239,16 @@ class ModelManager {
         model?.let { checkModelVersion(modelIdentifier, it) }
         if (model == null && globalCache.containsKey(modelIdentifier)) {
             model = globalCache[modelIdentifier]
-            models[modelPath] = model
-            modelsByUri[model!!.modelInfo.url!!] = model
+            models[modelPath] = model!!
+            modelsByUri[model.modelInfo.url!!] = model
         }
 
         if (model == null) {
             model = buildModel(modelIdentifier)
-            globalCache[modelIdentifier] = model
+            globalCache[modelIdentifier] = model!!
             checkModelVersion(modelIdentifier, model)
             models[modelPath] = model
-            modelsByUri[model!!.modelInfo.url!!] = model
+            modelsByUri[model.modelInfo.url!!] = model
         }
         return model
     }
@@ -264,20 +258,15 @@ class ModelManager {
             !(modelIdentifier.version != null &&
                 modelIdentifier.version != model!!.modelInfo.version)
         ) {
-            String.format(
-                Locale.US,
-                "Could not load model information for model %s, version %s because version %s is already loaded.",
-                modelIdentifier.id,
-                modelIdentifier.version,
-                model!!.modelInfo.version
-            )
+            "Could not load model information for model ${modelIdentifier.id}, version ${modelIdentifier.version}" +
+                " because version ${model!!.modelInfo.version} is already loaded."
         }
     }
 
     fun resolveModelByUri(namespaceUri: String): Model {
         return modelsByUri[namespaceUri]
             ?: throw IllegalArgumentException(
-                String.format(Locale.US, "Could not resolve model with namespace %s", namespaceUri)
+                "Could not resolve model with namespace $namespaceUri"
             )
     }
 }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/PriorityLibrarySourceLoader.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/PriorityLibrarySourceLoader.kt
index 38ae54e6f..b233536f4 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/PriorityLibrarySourceLoader.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/PriorityLibrarySourceLoader.kt
@@ -2,7 +2,6 @@ package org.cqframework.cql.cql2elm
 
 import java.io.InputStream
 import java.nio.file.Path
-import java.util.*
 import kotlin.collections.ArrayList
 import org.hl7.cql.model.NamespaceAware
 import org.hl7.cql.model.NamespaceManager
@@ -31,9 +30,7 @@ class PriorityLibrarySourceLoader : LibrarySourceLoader, NamespaceAware, PathAwa
     private var path: Path? = null
 
     override fun setPath(path: Path) {
-        require(path.toFile().isDirectory) {
-            String.format(Locale.US, "path '%s' is not a valid directory", path)
-        }
+        require(path.toFile().isDirectory) { "path '$path' is not a valid directory" }
         this.path = path
         for (provider in getProviders()) {
             if (provider is PathAware) {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringEscapeUtils.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringEscapeUtils.kt
index 116a60495..94759fd0b 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringEscapeUtils.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringEscapeUtils.kt
@@ -50,7 +50,8 @@ object StringEscapeUtils {
                     // '\u0020'..'\u007E' are printable ASCII characters
                     ESCAPE_MAP[char]
                         ?: if (char !in '\u0020'..'\u007E') {
-                            "\\u%04x".format(char.code)
+                            @Suppress("MagicNumber")
+                            "\\u${char.code.toString(HEX_RADIX).padStart(4, '0')}"
                         } else {
                             char
                         }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringLibrarySourceProvider.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringLibrarySourceProvider.kt
index 87a88f259..b59850529 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringLibrarySourceProvider.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/StringLibrarySourceProvider.kt
@@ -2,7 +2,6 @@ package org.cqframework.cql.cql2elm
 
 import java.io.ByteArrayInputStream
 import java.io.InputStream
-import java.util.*
 import kotlin.collections.ArrayList
 import org.hl7.elm.r1.VersionedIdentifier
 
@@ -28,14 +27,10 @@ class StringLibrarySourceProvider(private val libraries: List<String>) : Library
                 matches.add(library)
             }
         }
-        if (matches.size > 1) {
-            throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Multiple libraries for id : %s resolved.%nEnsure that there are no duplicates in the input set.",
-                    libraryIdentifier.toString()
-                )
-            )
+        require(matches.size <= 1) {
+            """"Multiple libraries for id : $libraryIdentifier resolved.
+                    Ensure that there are no duplicates in the input set."""
+                .trimMargin()
         }
         return if (matches.size == 1) ByteArrayInputStream(matches[0].toByteArray()) else null
     }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemFunctionResolver.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemFunctionResolver.kt
index a3b2ef408..294894ebe 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemFunctionResolver.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemFunctionResolver.kt
@@ -2,7 +2,6 @@
 
 package org.cqframework.cql.cql2elm
 
-import java.util.*
 import kotlin.collections.ArrayList
 import org.cqframework.cql.cql2elm.model.Invocation
 import org.cqframework.cql.cql2elm.model.invocation.*
@@ -11,11 +10,10 @@ import org.cqframework.cql.cql2elm.model.invocation.DateTimeInvocation.Companion
 import org.cqframework.cql.cql2elm.model.invocation.TimeInvocation.Companion.setTimeFieldsFromOperands
 import org.cqframework.cql.cql2elm.tracking.Trackable.resultType
 import org.cqframework.cql.cql2elm.tracking.Trackable.trackbacks
-import org.cqframework.cql.elm.IdObjectFactory
 import org.hl7.elm.r1.*
 
 @Suppress("LargeClass", "TooManyFunctions")
-class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFactory?) {
+class SystemFunctionResolver(private val builder: LibraryBuilder) {
     private val of = builder.objectFactory
 
     @Suppress("LongMethod", "CyclomaticComplexMethod", "NestedBlockDepth", "ReturnCount")
@@ -111,27 +109,25 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
                             builder.findConversion(
                                 op.resultType!!,
                                 builder.resolveTypeName("System", "Date")!!,
-                                true,
-                                false
+                                implicit = true,
+                                allowPromotionAndDemotion = false
                             )
                         val dateTimeConversion =
                             builder.findConversion(
                                 op.resultType!!,
                                 builder.resolveTypeName("System", "DateTime")!!,
-                                true,
-                                false
+                                implicit = true,
+                                allowPromotionAndDemotion = false
                             )
                         op =
                             when {
                                 dateConversion != null && dateTimeConversion != null -> {
                                     require(dateConversion.score != dateTimeConversion.score) {
-                                        "Ambiguous implicit conversion from %s to %s or %s."
-                                            .format(
-                                                Locale.US,
-                                                op.resultType.toString(),
-                                                dateConversion.toType.toString(),
-                                                dateTimeConversion.toType.toString()
-                                            )
+                                        """Ambiguous implicit conversion from
+                                            |${op.resultType} to ${dateConversion.toType}
+                                            |or ${dateTimeConversion}."""
+                                            .trimMargin()
+                                            .replace("\n", "")
                                     }
 
                                     if (dateConversion.score < dateTimeConversion.score) {
@@ -147,17 +143,14 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
                                 else -> {
                                     // ERROR
                                     throw IllegalArgumentException(
-                                        String.format(
-                                            Locale.US,
-                                            "Could not resolve call to operator %s with argument of type %s.",
-                                            functionRef.name,
-                                            op.resultType.toString()
-                                        )
+                                        """Could not resolve call to operator ${functionRef.name}
+                                           with argument of type ${op.resultType.toString()}."""
+                                            .trimIndent()
                                     )
                                 }
                             }
                     }
-                    ops.add(builder.enforceCompatible(patientBirthDateProperty, op.resultType)!!)
+                    ops.add(builder.enforceCompatible(patientBirthDateProperty, op.resultType))
                     ops.add(op)
                     return resolveCalculateAgeAt(
                         ops,
@@ -649,11 +642,7 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
             "ToConcept" -> convert.toType = builder.dataTypeToQName(sm.concept)
             else ->
                 throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Could not resolve call to system operator %s. Unknown conversion type.",
-                        functionRef.name
-                    )
+                    "Could not resolve call to system operator ${functionRef.name}. Unknown conversion type."
                 )
         }
         val invocation = ConvertInvocation(convert)
@@ -667,11 +656,7 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
             T::class.java.cast(of.javaClass.getMethod("create" + functionRef.name).invoke(of))
         } catch (@Suppress("TooGenericExceptionCaught") e: Exception) {
             throw CqlInternalException(
-                String.format(
-                    Locale.US,
-                    "Could not create instance of Element \"%s\"",
-                    functionRef.name
-                ),
+                "Could not create instance of Element \"${functionRef.name}\"",
                 if (functionRef.trackbacks.isNotEmpty()) functionRef.trackbacks[0] else null,
                 e
             )
@@ -724,12 +709,7 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
 
     private fun checkNumberOfOperands(functionRef: FunctionRef, expectedOperands: Int) {
         require(functionRef.operand.size == expectedOperands) {
-            String.format(
-                Locale.US,
-                "Could not resolve call to system operator %s.  Expected %d arguments.",
-                functionRef.name,
-                expectedOperands
-            )
+            "Could not resolve call to system operator ${functionRef.name}.  Expected $expectedOperands arguments."
         }
     }
 
@@ -747,10 +727,7 @@ class SystemFunctionResolver(private val builder: LibraryBuilder, of: IdObjectFa
                 name.contains("Minutes") -> DateTimePrecision.MINUTE
                 name.contains("Second") -> DateTimePrecision.SECOND
                 name.contains("Milliseconds") -> DateTimePrecision.MILLISECOND
-                else ->
-                    throw IllegalArgumentException(
-                        String.format(Locale.US, "Unknown precision '%s'.", name)
-                    )
+                else -> throw IllegalArgumentException("Unknown precision '$name'.")
             }
         }
     }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemMethodResolver.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemMethodResolver.kt
index 3c5faa1ad..54a179c2e 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemMethodResolver.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/SystemMethodResolver.kt
@@ -41,12 +41,7 @@ class SystemMethodResolver(
             actualCount = ctx.expression().size
         }
         require(actualCount == expectedCount) {
-            String.format(
-                Locale.US,
-                "Expected %s argument for method %s.",
-                Integer.valueOf(expectedCount).toString(),
-                functionName
-            )
+            "Expected ${Integer.valueOf(expectedCount)} argument for method $functionName."
         }
     }
 
@@ -233,34 +228,39 @@ class SystemMethodResolver(
         recurse: Boolean,
         dataTypes: MutableSet<DataType>
     ) {
-        if (dataType is ClassType) {
-            for (element in dataType.elements) {
-                val elementType =
-                    if (element.type is ListType) (element.type as ListType).elementType
-                    else element.type
-                dataTypes.add(elementType)
-                if (recurse) {
-                    gatherChildTypes(elementType, recurse, dataTypes)
+        when (dataType) {
+            is ClassType -> {
+                for (element in dataType.elements) {
+                    val elementType =
+                        if (element.type is ListType) (element.type as ListType).elementType
+                        else element.type
+                    dataTypes.add(elementType)
+                    if (recurse) {
+                        gatherChildTypes(elementType, true, dataTypes)
+                    }
                 }
             }
-        } else if (dataType is TupleType) {
-            for (element in dataType.elements) {
-                val elementType =
-                    if (element.type is ListType) (element.type as ListType).elementType
-                    else element.type
+            is TupleType -> {
+                for (element: TupleTypeElement in dataType.elements) {
+                    val elementType =
+                        if (element.type is ListType) (element.type as ListType).elementType
+                        else element.type
+                    dataTypes.add(elementType)
+                    if (recurse) {
+                        gatherChildTypes(elementType, true, dataTypes)
+                    }
+                }
+            }
+            is ListType -> {
+                val elementType = dataType.elementType
                 dataTypes.add(elementType)
                 if (recurse) {
-                    gatherChildTypes(elementType, recurse, dataTypes)
+                    gatherChildTypes(elementType, true, dataTypes)
                 }
             }
-        } else if (dataType is ListType) {
-            val elementType = dataType.elementType
-            dataTypes.add(elementType)
-            if (recurse) {
-                gatherChildTypes(elementType, recurse, dataTypes)
+            else -> {
+                dataTypes.add(builder.resolveTypeName("System.Any")!!)
             }
-        } else {
-            dataTypes.add(builder.resolveTypeName("System.Any")!!)
         }
     }
 
@@ -319,8 +319,8 @@ class SystemMethodResolver(
                     builder.ensureCompatibleTypes(target.resultType, argument.resultType!!)!!
                 val list = of.createList()
                 list.resultType = ListType(elementType)
-                list.element.add(builder.ensureCompatible(target, elementType)!!)
-                list.element.add(builder.ensureCompatible(argument, elementType)!!)
+                list.element.add(builder.ensureCompatible(target, elementType))
+                list.element.add(builder.ensureCompatible(argument, elementType))
                 val params = ArrayList<Expression>()
                 params.add(list)
                 builder.resolveFunction(null, "Flatten", params)
@@ -525,8 +525,8 @@ class SystemMethodResolver(
                     functionName,
                     getParams(target, ctx),
                     mustResolve,
-                    false,
-                    true
+                    allowPromotionAndDemotion = false,
+                    allowFluent = true
                 )
             }
         }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/TypeBuilder.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/TypeBuilder.kt
index 4c17ebeac..3e97726b9 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/TypeBuilder.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/TypeBuilder.kt
@@ -2,7 +2,6 @@
 
 package org.cqframework.cql.cql2elm
 
-import java.util.*
 import javax.xml.namespace.QName
 import kotlin.collections.ArrayList
 import org.cqframework.cql.cql2elm.model.Model
@@ -55,7 +54,7 @@ class TypeBuilder(private val of: IdObjectFactory, private val mr: ModelResolver
             is NamedType -> {
                 return of.createNamedTypeSpecifier()
                     .withName(dataTypeToQName(type))
-                    .withResultType(type) as TypeSpecifier
+                    .withResultType(type)
             }
             is ListType -> {
                 return listTypeToTypeSpecifier(type)
@@ -73,9 +72,7 @@ class TypeBuilder(private val of: IdObjectFactory, private val mr: ModelResolver
                 return typeParameterToTypeSpecifier(type)
             }
             else -> {
-                throw IllegalArgumentException(
-                    String.format(Locale.US, "Could not convert type %s to a type specifier.", type)
-                )
+                throw IllegalArgumentException("Could not convert type $type to a type specifier.")
             }
         }
     }
@@ -83,25 +80,24 @@ class TypeBuilder(private val of: IdObjectFactory, private val mr: ModelResolver
     private fun listTypeToTypeSpecifier(type: ListType): TypeSpecifier {
         return of.createListTypeSpecifier()
             .withElementType(dataTypeToTypeSpecifier(type.elementType))
-            .withResultType(type) as TypeSpecifier
+            .withResultType(type)
     }
 
     private fun intervalTypeToTypeSpecifier(type: IntervalType): TypeSpecifier {
         return of.createIntervalTypeSpecifier()
             .withPointType(dataTypeToTypeSpecifier(type.pointType))
-            .withResultType(type) as TypeSpecifier
+            .withResultType(type)
     }
 
     private fun tupleTypeToTypeSpecifier(type: TupleType): TypeSpecifier {
-        @Suppress("SpreadOperator")
         return of.createTupleTypeSpecifier()
-            .withElement(*tupleTypeElementsToTupleElementDefinitions(type.elements))
-            .withResultType(type) as TypeSpecifier
+            .withElement(tupleTypeElementsToTupleElementDefinitions(type.elements))
+            .withResultType(type)
     }
 
     private fun tupleTypeElementsToTupleElementDefinitions(
         elements: Iterable<TupleTypeElement>
-    ): Array<TupleElementDefinition> {
+    ): List<TupleElementDefinition> {
         val definitions: MutableList<TupleElementDefinition> = ArrayList()
         for (element: TupleTypeElement in elements) {
             definitions.add(
@@ -110,22 +106,21 @@ class TypeBuilder(private val of: IdObjectFactory, private val mr: ModelResolver
                     .withElementType(dataTypeToTypeSpecifier(element.type))
             )
         }
-        return definitions.toTypedArray<TupleElementDefinition>()
+        return definitions
     }
 
     private fun choiceTypeToTypeSpecifier(type: ChoiceType): TypeSpecifier {
-        @Suppress("SpreadOperator")
         return of.createChoiceTypeSpecifier()
-            .withChoice(*choiceTypeTypesToTypeSpecifiers(type))
-            .withResultType(type) as TypeSpecifier
+            .withChoice(choiceTypeTypesToTypeSpecifiers(type))
+            .withResultType(type)
     }
 
-    private fun choiceTypeTypesToTypeSpecifiers(choiceType: ChoiceType): Array<TypeSpecifier> {
+    private fun choiceTypeTypesToTypeSpecifiers(choiceType: ChoiceType): List<TypeSpecifier> {
         val specifiers: MutableList<TypeSpecifier> = ArrayList()
         for (type: DataType in choiceType.types) {
             specifiers.add(dataTypeToTypeSpecifier(type))
         }
-        return specifiers.toTypedArray<TypeSpecifier>()
+        return specifiers
     }
 
     private fun typeParameterToTypeSpecifier(type: TypeParameter): TypeSpecifier {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/elm/ElmEdit.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/elm/ElmEdit.kt
index 0036c9d4f..35702ab2e 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/elm/ElmEdit.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/elm/ElmEdit.kt
@@ -21,7 +21,7 @@ enum class ElmEdit : IElmEdit {
                 val x = annotations[i]
                 if (x is Annotation) {
                     x.s = null
-                    // Remove narrative but _not_ tags
+                    // Remove narrative but _not_ tags.
                     // Tags are necessary for `allowFluent` compiler resolution
                     // to work correctly
                     if (x.t.isEmpty()) {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/CompiledLibrary.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/CompiledLibrary.kt
index fbbaa147e..f94bc790b 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/CompiledLibrary.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/CompiledLibrary.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.model
 
-import java.util.*
 import kotlin.collections.ArrayList
 import kotlin.collections.HashMap
 import org.hl7.cql.model.DataType
@@ -32,11 +31,7 @@ class CompiledLibrary {
         val existingResolvedIdentifierContext = resolve(identifier)
         existingResolvedIdentifierContext.exactMatchElement?.let {
             throw IllegalArgumentException(
-                String.format(
-                    Locale.US,
-                    "Identifier %s is already in use in this library.",
-                    identifier
-                )
+                "Identifier $identifier is already in use in this library."
             )
         }
     }
@@ -97,25 +92,16 @@ class CompiledLibrary {
         // If this library has no identifier, the operator must not have an identifier
         operator.libraryName = operator.libraryName ?: identifier?.id
         require(operator.libraryName == identifier?.id) {
-            String.format(
-                Locale.US,
-                "Operator %s cannot be registered in library %s because it is defined in library %s.",
-                operator.name,
-                identifier?.id ?: "<anonymous>",
-                operator.libraryName
-            )
+            "Operator ${operator.name} cannot be registered in library ${identifier?.id ?: "<anonymous>"}" +
+                "because it is defined in library ${operator.libraryName}."
         }
     }
 
     @Suppress("UnusedPrivateMember")
     private fun ensureResultType(operator: Operator) {
         requireNotNull(operator.resultType) {
-            String.format(
-                Locale.US,
-                "Operator %s cannot be registered in library %s because it does not have a result type defined.",
-                operator.name,
-                identifier?.id ?: "<anonymous>"
-            )
+            """Operator ${operator.name} cannot be registered in library ${identifier?.id ?: "<anonymous>"}
+                    because it does not have a result type defined."""
         }
     }
 
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ConversionMap.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ConversionMap.kt
index 3c88bdb29..3f4c99a34 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ConversionMap.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ConversionMap.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.model
 
-import java.util.*
 import kotlin.collections.ArrayList
 import kotlin.collections.HashMap
 import org.hl7.cql.model.ChoiceType
@@ -64,24 +63,14 @@ class ConversionMap {
         if (conversion.isGeneric) {
             val conversions = genericConversions
             check(!hasConversion(conversion, conversions)) {
-                String.format(
-                    Locale.US,
-                    "Conversion from %s to %s is already defined.",
-                    conversion.fromType.toString(),
-                    conversion.toType.toString()
-                )
+                "Conversion from ${conversion.fromType} to ${conversion.toType} is already defined."
             }
 
             conversions.add(conversion)
         } else {
             val conversions = getConversions(conversion.fromType)
             check(!hasConversion(conversion, conversions)) {
-                String.format(
-                    Locale.US,
-                    "Conversion from %s to %s is already defined.",
-                    conversion.fromType.toString(),
-                    conversion.toType.toString()
-                )
+                "Conversion from ${conversion.fromType} to ${conversion.toType} is already defined."
             }
 
             conversions.add(conversion)
@@ -321,13 +310,7 @@ class ConversionMap {
                 } else
                     require(newScore != score) {
                         // ERROR
-                        String.format(
-                            Locale.US,
-                            "Ambiguous implicit conversion from %s to %s or %s.",
-                            fromType.toString(),
-                            result!!.toType.toString(),
-                            conversion.toType.toString()
-                        )
+                        "Ambiguous implicit conversion from $fromType to ${result!!.toType} or ${conversion.toType}."
                     }
             }
         }
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/InstantiationContextImpl.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/InstantiationContextImpl.kt
index eb59e055b..538b7ff52 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/InstantiationContextImpl.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/InstantiationContextImpl.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.model
 
-import java.util.*
 import kotlin.collections.ArrayList
 import org.hl7.cql.model.DataType
 import org.hl7.cql.model.InstantiationContext
@@ -144,11 +143,7 @@ class InstantiationContextImpl(
         val result =
             typeMap[parameter]
                 ?: throw IllegalArgumentException(
-                    String.format(
-                        Locale.US,
-                        "Could not resolve type parameter %s.",
-                        parameter.identifier
-                    )
+                    "Could not resolve type parameter ${parameter.identifier}."
                 )
 
         return result
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/Model.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/Model.kt
index 33703477c..fcb5e5e07 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/Model.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/Model.kt
@@ -83,12 +83,7 @@ open class Model(val modelInfo: ModelInfo, modelManager: ModelManager?) {
         // then throw an error
         require(!mustResolve) {
             // ERROR:
-            String.format(
-                Locale.US,
-                "Could not resolve context name %s in model %s.",
-                contextName,
-                modelInfo.name
-            )
+            "Could not resolve context name $contextName in model ${modelInfo.name}."
         }
 
         return null
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ModelImporter.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ModelImporter.kt
index a28c8d71e..e8f689b9b 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ModelImporter.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ModelImporter.kt
@@ -114,7 +114,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
             val contextType = resolveTypeSpecifier(c.contextType!!)
             require(contextType is ClassType) {
                 // ERROR:
-                String.format(Locale.US, "Model context %s must be a class type.", c.name)
+                "Model context ${c.name} must be a class type."
             }
             val modelContext =
                 ModelContext(
@@ -202,7 +202,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
                 qualifier = modelInfo.name
             }
 
-            val qualifiedTypeName = String.format(Locale.US, "%s.%s", qualifier, typeSpecifier.name)
+            val qualifiedTypeName = "$qualifier.${typeSpecifier.name}"
             return resolveTypeName(qualifiedTypeName)
         }
 
@@ -277,11 +277,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
             val typeInfo =
                 lookupTypeInfo(ensureUnqualified(typeName))
                     ?: throw IllegalArgumentException(
-                        String.format(
-                            Locale.US,
-                            "Could not resolve type info for type name %s.",
-                            typeName
-                        )
+                        "Could not resolve type info for type name $typeName."
                     )
 
             result = resolveTypeInfo(typeInfo)
@@ -338,9 +334,9 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
     // qualified with the
     // model name
     private fun ensureQualified(name: String): String {
-        val qualifier = String.format(Locale.US, "%s.", modelInfo.name)
+        val qualifier = "${modelInfo.name}."
         if (!name.startsWith(qualifier)) {
-            return String.format(Locale.US, "%s%s", qualifier, name)
+            return "$qualifier$name"
         }
 
         return name
@@ -350,7 +346,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
     // qualified with the
     // model name
     private fun ensureUnqualified(name: String): String {
-        if (name.startsWith(String.format(Locale.US, "%s.", modelInfo.name))) {
+        if (name.startsWith("${modelInfo.name}.")) {
             return name.substring(name.indexOf('.') + 1)
         }
 
@@ -361,11 +357,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
         val qualifiedTypeName = ensureQualified(t.name!!)
         val lookupType = lookupType(qualifiedTypeName)
         require(lookupType !is ClassType) {
-            String.format(
-                Locale.US,
-                "Expected instance of SimpleType but found instance of %s instead.",
-                lookupType
-            )
+            "Expected instance of SimpleType but found instance of $lookupType instead."
         }
 
         var result = lookupType(qualifiedTypeName) as SimpleType?
@@ -670,9 +662,7 @@ class ModelImporter(val modelInfo: ModelInfo, val modelManager: ModelManager?) {
             }
         }
 
-        throw IllegalArgumentException(
-            String.format(Locale.US, "Could not resolve context name %s.", contextName)
-        )
+        throw IllegalArgumentException("Could not resolve context name $contextName.")
     }
 
     private fun resolveRelationship(relationshipInfo: RelationshipInfo): Relationship {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/OperatorEntry.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/OperatorEntry.kt
index 51b13078b..a381fd782 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/OperatorEntry.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/OperatorEntry.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.model
 
-import java.util.*
 import kotlin.collections.ArrayList
 import kotlin.collections.HashMap
 import org.hl7.cql.model.ChoiceType
@@ -224,12 +223,7 @@ class OperatorEntry(val name: String) {
             requireNotNull(node) { "node is null." }
 
             require(!signatures.containsKey(node.signature)) {
-                String.format(
-                    Locale.US,
-                    "Operator %s already has a registration for signature: %s.",
-                    node.operator.name,
-                    node.signature.toString()
-                )
+                "Operator ${node.operator.name} already has a registration for signature: ${node.signature}."
             }
 
             var added = false
@@ -307,12 +301,7 @@ class OperatorEntry(val name: String) {
 
     private fun addGenericOperator(operator: GenericOperator) {
         require(!genericOperators.containsKey(operator.signature)) {
-            String.format(
-                Locale.US,
-                "Operator %s already has a generic registration for signature: %s.",
-                name,
-                operator.signature.toString()
-            )
+            "Operator $name already has a generic registration for signature: ${operator.signature}."
         }
 
         genericOperators[operator.signature] = operator
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/QueryContext.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/QueryContext.kt
index 5334cefc0..2869710ac 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/QueryContext.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/QueryContext.kt
@@ -48,7 +48,7 @@ class QueryContext {
         lets[let.identifier!!] = let
     }
 
-    fun removeLetClause(let: LetClause) {
+    private fun removeLetClause(let: LetClause) {
         lets.remove(let.identifier)
     }
 
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ResolvedIdentifierContext.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ResolvedIdentifierContext.kt
index 322c97773..b46652d21 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ResolvedIdentifierContext.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/ResolvedIdentifierContext.kt
@@ -40,12 +40,7 @@ private constructor(
     fun warnCaseInsensitiveIfApplicable(): String? {
         if (element != null && !isExactMatch) {
             return getName(element)?.let {
-                String.format(
-                    Locale.US,
-                    "Could not find identifier: [%s].  Did you mean [%s]?",
-                    identifier,
-                    it
-                )
+                "Could not find identifier: [$identifier].  Did you mean [$it]?"
             }
         }
 
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/SystemLibraryHelper.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/SystemLibraryHelper.kt
index 93c264eb2..e3d245e72 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/SystemLibraryHelper.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/model/SystemLibraryHelper.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.model
 
-import java.util.*
 import org.cqframework.cql.cql2elm.TypeBuilder
 import org.cqframework.cql.cql2elm.tracking.Trackable.resultType
 import org.hl7.cql.model.IntervalType
@@ -2947,7 +2946,7 @@ object SystemLibraryHelper {
         var n = 0
         for (dataType in operator.signature.operandTypes) {
             n++
-            val od = OperandDef().withName(String.format(Locale.US, "param%d", n))
+            val od = OperandDef().withName("param${n}")
             if (dataType is NamedType) {
                 od.operandType = tb.dataTypeToQName(dataType)
             } else {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessor.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessor.kt
index 6ca89b2b9..7f51863b6 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessor.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessor.kt
@@ -2,7 +2,6 @@
 
 package org.cqframework.cql.cql2elm.preprocessor
 
-import java.util.*
 import kotlin.collections.ArrayList
 import org.antlr.v4.kotlinruntime.Recognizer
 import org.antlr.v4.kotlinruntime.TokenStream
@@ -135,13 +134,8 @@ class CqlPreprocessor(libraryBuilder: LibraryBuilder, tokenStream: TokenStream)
             if (ctx.localIdentifier() == null) unqualifiedIdentifier
             else parseString(ctx.localIdentifier())!!
         require(localIdentifier == unqualifiedIdentifier) {
-            String.format(
-                Locale.US,
-                @Suppress("MaxLineLength")
-                "Local identifiers for models must be the same as the name of the model in this release of the translator (Model %s, Called %s)",
-                unqualifiedIdentifier,
-                localIdentifier
-            )
+            """Local identifiers for models must be the same as the name of the model 
+                in this release of the translator (Model $unqualifiedIdentifier, Called $localIdentifier)"""
         }
 
         // This has the side effect of initializing
@@ -238,7 +232,7 @@ class CqlPreprocessor(libraryBuilder: LibraryBuilder, tokenStream: TokenStream)
         val modelIdentifier = getModelIdentifier(qualifiers)
         val identifier =
             getTypeIdentifier(qualifiers, parseString(ctx.referentialOrTypeNameIdentifier())!!)
-        val typeSpecifierKey = String.format(Locale.US, "%s:%s", modelIdentifier, identifier)
+        val typeSpecifierKey = "$modelIdentifier:$identifier"
         val resultType = libraryBuilder.resolveTypeName(modelIdentifier, identifier)
         if (null == resultType) {
             libraryBuilder.addNamedTypeSpecifierResult(
@@ -246,12 +240,7 @@ class CqlPreprocessor(libraryBuilder: LibraryBuilder, tokenStream: TokenStream)
                 ResultWithPossibleError.withError()
             )
             throw CqlCompilerException(
-                String.format(
-                    Locale.US,
-                    "Could not find type for model: %s and name: %s",
-                    modelIdentifier,
-                    identifier
-                )
+                "Could not find type for model: $modelIdentifier and name: $identifier"
             )
         }
         val result =
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessorElmCommonVisitor.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessorElmCommonVisitor.kt
index c4f93d3db..b0672cb01 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessorElmCommonVisitor.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/CqlPreprocessorElmCommonVisitor.kt
@@ -42,10 +42,8 @@ abstract class CqlPreprocessorElmCommonVisitor(
     @JvmField protected val libraryBuilder: LibraryBuilder,
     protected val tokenStream: TokenStream
 ) : cqlBaseVisitor<Any?>() {
-    @JvmField
-    protected val of: IdObjectFactory =
-        requireNotNull(libraryBuilder.objectFactory) { "libraryBuilder.objectFactory required" }
-    protected val af = ObjectFactory()
+    @JvmField protected val of: IdObjectFactory = libraryBuilder.objectFactory
+    private val af = ObjectFactory()
     protected var implicitContextCreated = false
     protected var currentContext = "Unfiltered"
     @JvmField protected var chunks = Stack<Chunk>()
@@ -87,17 +85,11 @@ abstract class CqlPreprocessorElmCommonVisitor(
             // ERROR:
             try {
                 o = super.visit(tree)
-                if (o is Element) {
-                    if (o.localId == null) {
-                        throw CqlInternalException(
-                            String.format(
-                                Locale.US,
-                                "Internal translator error. 'localId' was not assigned for Element \"%s\"",
-                                o.javaClass.name
-                            ),
-                            getTrackBack(tree)
-                        )
-                    }
+                if (o is Element && o.localId == null) {
+                    throw CqlInternalException(
+                        "Internal translator error. 'localId' was not assigned for Element \"${o.javaClass.name}\"",
+                        getTrackBack(tree)
+                    )
                 }
             } catch (e: CqlIncludeException) {
                 val translatorException = CqlCompilerException(e.message, getTrackBack(tree), e)
@@ -285,7 +277,7 @@ abstract class CqlPreprocessorElmCommonVisitor(
                         o is ExpressionDef
                 ) {
                     val a = getAnnotation(o)
-                    if (a == null || a.s == null) {
+                    if (a?.s == null) {
                         // Add header information (comments prior to the definition)
                         val definitionInfo = libraryInfo.resolveDefinition(tree)
                         if (definitionInfo?.headerInterval != null) {
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/LibraryInfo.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/LibraryInfo.kt
index 1af450d0d..25d695c8d 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/LibraryInfo.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/preprocessor/LibraryInfo.kt
@@ -153,7 +153,7 @@ class LibraryInfo(
         addDefinition(functionDefinition)
     }
 
-    fun resolveFunctionReference(identifier: String): Iterable<FunctionDefinitionInfo>? {
+    fun resolveFunctionReference(identifier: String): List<FunctionDefinitionInfo>? {
         return functionDefinitions[identifier]
     }
 
diff --git a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/tracking/TrackBack.kt b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/tracking/TrackBack.kt
index 43ecf0576..d4ae90cfd 100644
--- a/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/tracking/TrackBack.kt
+++ b/Src/java/cql-to-elm/src/main/kotlin/org/cqframework/cql/cql2elm/tracking/TrackBack.kt
@@ -1,6 +1,5 @@
 package org.cqframework.cql.cql2elm.tracking
 
-import java.util.*
 import org.hl7.elm.r1.VersionedIdentifier
 
 data class TrackBack(
@@ -28,8 +27,7 @@ data class TrackBack(
     }
 
     fun toLocator(): String {
-        return if (startLine == endLine && startChar == endChar)
-            String.format(Locale.US, "%s:%s", startLine, startChar)
-        else String.format(Locale.US, "%s:%s-%s:%s", startLine, startChar, endLine, endChar)
+        return if (startLine == endLine && startChar == endChar) "$startLine:$startChar"
+        else "$startLine:$startChar-$endLine:$endChar"
     }
 }
diff --git a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/evaluating/SimpleElmEngine.kt b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/evaluating/SimpleElmEngine.kt
index 68062f205..a0519f67d 100644
--- a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/evaluating/SimpleElmEngine.kt
+++ b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/evaluating/SimpleElmEngine.kt
@@ -91,8 +91,7 @@ etc.)
 class SimpleElmEngine {
     private fun literalsEqual(left: Literal?, right: Literal?): Boolean {
         return (left == null && right == null) ||
-            (left != null &&
-                left.valueType != null &&
+            (left?.valueType != null &&
                 left.valueType == right!!.valueType &&
                 stringsEqual(left.value, right.value))
     }
@@ -109,7 +108,7 @@ class SimpleElmEngine {
         return expressionsEqual(left, right)
     }
 
-    fun decimalsEqual(left: BigDecimal?, right: BigDecimal?): Boolean {
+    private fun decimalsEqual(left: BigDecimal?, right: BigDecimal?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -121,7 +120,7 @@ class SimpleElmEngine {
         return left == right
     }
 
-    fun quantitiesEqual(left: Quantity?, right: Quantity?): Boolean {
+    private fun quantitiesEqual(left: Quantity?, right: Quantity?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -149,7 +148,7 @@ class SimpleElmEngine {
         return (left == null && right == null) || (left != null && left == right)
     }
 
-    fun systemsEqual(left: CodeSystemRef?, right: CodeSystemRef?): Boolean {
+    private fun systemsEqual(left: CodeSystemRef?, right: CodeSystemRef?): Boolean {
         // TODO: Needs to do the comparison on the URI, but I don't want to have to resolve here
         return (left == null && right == null) ||
             (left != null &&
@@ -157,7 +156,7 @@ class SimpleElmEngine {
                 stringsEqual(left.name, right.name))
     }
 
-    fun valueSetsEqual(left: ValueSetRef?, right: ValueSetRef?): Boolean {
+    private fun valueSetsEqual(left: ValueSetRef?, right: ValueSetRef?): Boolean {
         // TODO: Needs to do the comparison on the URI, but I don't want to have to resolve here
         return (left == null && right == null) ||
             (left != null &&
@@ -220,26 +219,15 @@ class SimpleElmEngine {
         // TupleTypeSpecifier
         if (left is TupleTypeSpecifier) {
             if (right is TupleTypeSpecifier) {
-                val leftArg = left
-                val rightArg = right
-                if (
-                    leftArg.element != null &&
-                        rightArg.element != null &&
-                        leftArg.element!!.size == rightArg.element!!.size
-                ) {
-                    for (i in leftArg.element!!.indices) {
-                        val leftElement = leftArg.element!![i]
-                        val rightElement = rightArg.element!![i]
+                if (left.element.size == right.element.size) {
+                    for (i in left.element.indices) {
+                        val leftElement = left.element[i]
+                        val rightElement = right.element[i]
                         if (
                             !typeSpecifiersEqual(
-                                leftElement!!.elementType,
-                                rightElement!!.elementType
-                            ) ||
-                                !typeSpecifiersEqual(
-                                    leftElement.elementType,
-                                    rightElement.elementType
-                                ) ||
-                                !stringsEqual(leftElement.name, rightElement.name)
+                                leftElement.elementType,
+                                rightElement.elementType
+                            ) || !stringsEqual(leftElement.name, rightElement.name)
                         ) {
                             return false
                         }
@@ -257,30 +245,20 @@ class SimpleElmEngine {
         // ChoiceTypeSpecifier
         if (left is ChoiceTypeSpecifier) {
             if (right is ChoiceTypeSpecifier) {
-                val leftArg = left
-                val rightArg = right
-                if (
-                    leftArg.choice != null &&
-                        rightArg.choice != null &&
-                        leftArg.choice!!.size == rightArg.choice!!.size
-                ) {
-                    for (i in leftArg.choice!!.indices) {
-                        val leftType = leftArg.choice!![i]
-                        val rightType = rightArg.choice!![i]
+                if (left.choice.size == right.choice.size) {
+                    for (i in left.choice.indices) {
+                        val leftType = left.choice[i]
+                        val rightType = right.choice[i]
                         if (!typeSpecifiersEqual(leftType, rightType)) {
                             return false
                         }
                     }
                 }
 
-                if (
-                    leftArg.choice != null &&
-                        rightArg.choice != null &&
-                        leftArg.choice!!.size == rightArg.choice!!.size
-                ) {
-                    for (i in leftArg.choice!!.indices) {
-                        val leftType = leftArg.choice!![i]
-                        val rightType = rightArg.choice!![i]
+                if (left.choice.size == right.choice.size) {
+                    for (i in left.choice.indices) {
+                        val leftType = left.choice[i]
+                        val rightType = right.choice[i]
                         if (!typeSpecifiersEqual(leftType, rightType)) {
                             return false
                         }
@@ -299,7 +277,7 @@ class SimpleElmEngine {
         return false
     }
 
-    fun expressionsEqual(left: Expression?, right: Expression?): Boolean {
+    private fun expressionsEqual(left: Expression?, right: Expression?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -318,12 +296,10 @@ class SimpleElmEngine {
 
         if (left is Date) {
             if (right is Date) {
-                val leftDate = left
-                val rightDate = right
 
-                return integersEqual(leftDate.year, rightDate.year) &&
-                    integersEqual(leftDate.month, rightDate.month) &&
-                    integersEqual(leftDate.day, rightDate.day)
+                return integersEqual(left.year, right.year) &&
+                    integersEqual(left.month, right.month) &&
+                    integersEqual(left.day, right.day)
             }
 
             return false
@@ -331,13 +307,11 @@ class SimpleElmEngine {
 
         if (left is Time) {
             if (right is Time) {
-                val leftTime = left
-                val rightTime = right
 
-                return integersEqual(leftTime.hour, rightTime.hour) &&
-                    integersEqual(leftTime.minute, rightTime.minute) &&
-                    integersEqual(leftTime.second, rightTime.second) &&
-                    integersEqual(leftTime.millisecond, rightTime.millisecond)
+                return integersEqual(left.hour, right.hour) &&
+                    integersEqual(left.minute, right.minute) &&
+                    integersEqual(left.second, right.second) &&
+                    integersEqual(left.millisecond, right.millisecond)
             }
 
             return false
@@ -345,17 +319,15 @@ class SimpleElmEngine {
 
         if (left is DateTime) {
             if (right is DateTime) {
-                val leftDateTime = left
-                val rightDateTime = right
 
-                return integersEqual(leftDateTime.year, rightDateTime.year) &&
-                    integersEqual(leftDateTime.month, rightDateTime.month) &&
-                    integersEqual(leftDateTime.day, rightDateTime.day) &&
-                    integersEqual(leftDateTime.hour, rightDateTime.hour) &&
-                    integersEqual(leftDateTime.minute, rightDateTime.minute) &&
-                    integersEqual(leftDateTime.second, rightDateTime.second) &&
-                    integersEqual(leftDateTime.millisecond, rightDateTime.millisecond) &&
-                    decimalsEqual(leftDateTime.timezoneOffset, rightDateTime.timezoneOffset)
+                return integersEqual(left.year, right.year) &&
+                    integersEqual(left.month, right.month) &&
+                    integersEqual(left.day, right.day) &&
+                    integersEqual(left.hour, right.hour) &&
+                    integersEqual(left.minute, right.minute) &&
+                    integersEqual(left.second, right.second) &&
+                    integersEqual(left.millisecond, right.millisecond) &&
+                    decimalsEqual(left.timezoneOffset, right.timezoneOffset)
             }
 
             return false
@@ -363,21 +335,13 @@ class SimpleElmEngine {
 
         if (left is Interval) {
             if (right is Interval) {
-                val leftInterval = left
-                val rightInterval = right
 
-                return booleansEqual(
-                    leftInterval.lowClosedExpression,
-                    rightInterval.lowClosedExpression
-                ) &&
-                    dateTimesEqual(leftInterval.low, rightInterval.low) &&
-                    leftInterval.isLowClosed() == rightInterval.isLowClosed() &&
-                    booleansEqual(
-                        leftInterval.highClosedExpression,
-                        rightInterval.highClosedExpression
-                    ) &&
-                    dateTimesEqual(leftInterval.high, rightInterval.high) &&
-                    leftInterval.isHighClosed() == rightInterval.isHighClosed()
+                return booleansEqual(left.lowClosedExpression, right.lowClosedExpression) &&
+                    dateTimesEqual(left.low, right.low) &&
+                    left.isLowClosed() == right.isLowClosed() &&
+                    booleansEqual(left.highClosedExpression, right.highClosedExpression) &&
+                    dateTimesEqual(left.high, right.high) &&
+                    left.isHighClosed() == right.isHighClosed()
             }
 
             return false
@@ -388,10 +352,8 @@ class SimpleElmEngine {
         // local parameter reference
         if (left is ParameterRef) {
             if (right is ParameterRef) {
-                val leftParameter = left
-                val rightParameter = right
-                return stringsEqual(leftParameter.libraryName, rightParameter.libraryName) &&
-                    stringsEqual(leftParameter.name, rightParameter.name)
+                return stringsEqual(left.libraryName, right.libraryName) &&
+                    stringsEqual(left.name, right.name)
             }
 
             return false
@@ -415,11 +377,9 @@ class SimpleElmEngine {
 
         if (left is ConceptRef) {
             if (right is ConceptRef) {
-                val leftConcept = left
-                val rightConcept = right
                 // TODO: Needs to do the comparison on the URI, but I don't want to resolve here
-                return stringsEqual(leftConcept.libraryName, rightConcept.libraryName) &&
-                    stringsEqual(leftConcept.name, rightConcept.name)
+                return stringsEqual(left.libraryName, right.libraryName) &&
+                    stringsEqual(left.name, right.name)
             }
 
             return false
@@ -427,11 +387,9 @@ class SimpleElmEngine {
 
         if (left is CodeRef) {
             if (right is CodeRef) {
-                val leftCode = left
-                val rightCode = right
                 // TODO: Needs to do the comparison on the URI, but I don't want to resolve here
-                return stringsEqual(leftCode.libraryName, rightCode.libraryName) &&
-                    stringsEqual(leftCode.name, rightCode.name)
+                return stringsEqual(left.libraryName, right.libraryName) &&
+                    stringsEqual(left.name, right.name)
             }
 
             return false
@@ -439,10 +397,8 @@ class SimpleElmEngine {
 
         if (left is Code) {
             if (right is Code) {
-                val leftCode = left
-                val rightCode = right
-                return stringsEqual(leftCode.code, rightCode.code) &&
-                    systemsEqual(leftCode.system, rightCode.system)
+                return stringsEqual(left.code, right.code) &&
+                    systemsEqual(left.system, right.system)
             }
 
             return false
@@ -450,14 +406,10 @@ class SimpleElmEngine {
 
         if (left is Concept) {
             if (right is Concept) {
-                val leftConcept = left
-                val rightConcept = right
-                if (leftConcept.code != null && rightConcept.code != null) {
-                    for (lc in leftConcept.code!!) {
-                        for (rc in rightConcept.code!!) {
-                            if (codesEqual(lc, rc)) {
-                                return true
-                            }
+                for (lc in left.code) {
+                    for (rc in right.code) {
+                        if (codesEqual(lc, rc)) {
+                            return true
                         }
                     }
                 }
@@ -467,15 +419,11 @@ class SimpleElmEngine {
         }
 
         if (left is List) {
-            if (right is List) {
-                val leftList = left
-                val rightList = right
-                // TODO: Potentially use a hashSet to avoid order-dependence here
-                if (leftList.element!!.size == rightList.element!!.size) {
-                    for (i in leftList.element!!.indices) {
-                        if (!codesEqual(leftList.element!![i], rightList.element!![i])) {
-                            return false
-                        }
+            // TODO: Potentially use a hashSet to avoid order-dependence here
+            if (right is List && left.element.size == right.element.size) {
+                for (i in left.element.indices) {
+                    if (!codesEqual(left.element[i], right.element[i])) {
+                        return false
                     }
                 }
             }
@@ -518,14 +466,9 @@ class SimpleElmEngine {
         // InCodeSystem
         if (left is InCodeSystem) {
             if (right is InCodeSystem) {
-                val inCodeSystemLeft = left
-                val inCodeSystemRight = right
-                return expressionsEqual(inCodeSystemLeft.code, inCodeSystemRight.code) &&
-                    systemsEqual(inCodeSystemLeft.codesystem, inCodeSystemRight.codesystem) &&
-                    expressionsEqual(
-                        inCodeSystemLeft.codesystemExpression,
-                        inCodeSystemRight.codesystemExpression
-                    )
+                return expressionsEqual(left.code, right.code) &&
+                    systemsEqual(left.codesystem, right.codesystem) &&
+                    expressionsEqual(left.codesystemExpression, right.codesystemExpression)
             }
 
             return false
@@ -534,14 +477,9 @@ class SimpleElmEngine {
         // AnyInCodeSystem
         if (left is AnyInCodeSystem) {
             if (right is AnyInCodeSystem) {
-                val anyInCodeSystemLeft = left
-                val anyInCodeSystemRight = right
-                return expressionsEqual(anyInCodeSystemLeft.codes, anyInCodeSystemRight.codes) &&
-                    systemsEqual(anyInCodeSystemLeft.codesystem, anyInCodeSystemRight.codesystem) &&
-                    expressionsEqual(
-                        anyInCodeSystemLeft.codesystemExpression,
-                        anyInCodeSystemRight.codesystemExpression
-                    )
+                return expressionsEqual(left.codes, right.codes) &&
+                    systemsEqual(left.codesystem, right.codesystem) &&
+                    expressionsEqual(left.codesystemExpression, right.codesystemExpression)
             }
 
             return false
@@ -550,11 +488,9 @@ class SimpleElmEngine {
         // InValueSet
         if (left is InValueSet) {
             if (right is InValueSet) {
-                val inLeft = left
-                val inRight = right
-                return expressionsEqual(inLeft.code, inRight.code) &&
-                    valueSetsEqual(inLeft.valueset, inRight.valueset) &&
-                    expressionsEqual(inLeft.valuesetExpression, inRight.valuesetExpression)
+                return expressionsEqual(left.code, right.code) &&
+                    valueSetsEqual(left.valueset, right.valueset) &&
+                    expressionsEqual(left.valuesetExpression, right.valuesetExpression)
             }
 
             return false
@@ -563,11 +499,9 @@ class SimpleElmEngine {
         // AnyInValueSet
         if (left is AnyInValueSet) {
             if (right is AnyInValueSet) {
-                val inLeft = left
-                val inRight = right
-                return expressionsEqual(inLeft.codes, inRight.codes) &&
-                    valueSetsEqual(inLeft.valueset, inRight.valueset) &&
-                    expressionsEqual(inLeft.valuesetExpression, inRight.valuesetExpression)
+                return expressionsEqual(left.codes, right.codes) &&
+                    valueSetsEqual(left.valueset, right.valueset) &&
+                    expressionsEqual(left.valuesetExpression, right.valuesetExpression)
             }
 
             return false
@@ -576,10 +510,8 @@ class SimpleElmEngine {
         // CalculateAge
         if (left is CalculateAge) {
             if (right is CalculateAge) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.operand, rightArg.operand) &&
-                    leftArg.precision == rightArg.precision
+                return expressionsEqual(left.operand, right.operand) &&
+                    left.precision == right.precision
             }
 
             return false
@@ -588,11 +520,7 @@ class SimpleElmEngine {
         // Subsumes
         if (left is Subsumes) {
             if (right is Subsumes) {
-                if (operandsEqual(left, right)) {
-                    return true
-                }
-
-                return false
+                return operandsEqual(left, right)
             }
 
             return false
@@ -601,11 +529,7 @@ class SimpleElmEngine {
         // SubsumedBy
         if (left is SubsumedBy) {
             if (right is SubsumedBy) {
-                if (operandsEqual(left, right)) {
-                    return true
-                }
-
-                return false
+                return operandsEqual(left, right)
             }
 
             return false
@@ -645,26 +569,20 @@ class SimpleElmEngine {
         // Case
         if (left is Case) {
             if (right is Case) {
-                val leftArg = left
-                val rightArg = right
-                if (!expressionsEqual(leftArg.comparand, rightArg.comparand)) {
+                if (!expressionsEqual(left.comparand, right.comparand)) {
                     return false
                 }
 
-                if (!expressionsEqual(leftArg.`else`, rightArg.`else`)) {
+                if (!expressionsEqual(left.`else`, right.`else`)) {
                     return false
                 }
 
-                if (
-                    leftArg.caseItem != null &&
-                        rightArg.caseItem != null &&
-                        (leftArg.caseItem!!.size == rightArg.caseItem!!.size)
-                ) {
-                    for (i in leftArg.caseItem!!.indices) {
-                        val leftCaseItem = leftArg.caseItem!![i]
-                        val rightCaseItem = rightArg.caseItem!![i]
+                if (left.caseItem.size == right.caseItem.size) {
+                    for (i in left.caseItem.indices) {
+                        val leftCaseItem = left.caseItem[i]
+                        val rightCaseItem = right.caseItem[i]
                         if (
-                            !expressionsEqual(leftCaseItem!!.`when`, rightCaseItem!!.`when`) ||
+                            !expressionsEqual(leftCaseItem.`when`, rightCaseItem.`when`) ||
                                 !expressionsEqual(leftCaseItem.then, rightCaseItem.then)
                         ) {
                             return false
@@ -690,23 +608,17 @@ class SimpleElmEngine {
         }
 
         // FunctionRef
-        if (left is FunctionRef) {
-            if (right is FunctionRef) {
-                val leftArg = left
-                val rightArg = right
-                return stringsEqual(leftArg.libraryName, rightArg.libraryName) &&
-                    stringsEqual(leftArg.name, rightArg.name) &&
-                    operandsEqual(leftArg, rightArg)
-            }
+        if (left is FunctionRef && right is FunctionRef) {
+            return stringsEqual(left.libraryName, right.libraryName) &&
+                stringsEqual(left.name, right.name) &&
+                operandsEqual(left, right)
         }
 
         // ExpressionRef
         if (left is ExpressionRef) {
             if (right is ExpressionRef) {
-                val leftArg = left
-                val rightArg = right
-                return stringsEqual(leftArg.libraryName, rightArg.libraryName) &&
-                    stringsEqual(leftArg.name, rightArg.name)
+                return stringsEqual(left.libraryName, right.libraryName) &&
+                    stringsEqual(left.name, right.name)
             }
 
             return false
@@ -715,11 +627,9 @@ class SimpleElmEngine {
         // Filter
         if (left is Filter) {
             if (right is Filter) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.condition, rightArg.condition) &&
-                    stringsEqual(leftArg.scope, rightArg.scope)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.condition, right.condition) &&
+                    stringsEqual(left.scope, right.scope)
             }
 
             return false
@@ -728,11 +638,9 @@ class SimpleElmEngine {
         // ForEach
         if (left is ForEach) {
             if (right is ForEach) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.element, rightArg.element) &&
-                    stringsEqual(leftArg.scope, rightArg.scope)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.element, right.element) &&
+                    stringsEqual(left.scope, right.scope)
             }
 
             return false
@@ -741,10 +649,8 @@ class SimpleElmEngine {
         // IdentifierRef
         if (left is IdentifierRef) {
             if (right is IdentifierRef) {
-                val leftArg = left
-                val rightArg = right
-                return stringsEqual(leftArg.libraryName, rightArg.libraryName) &&
-                    stringsEqual(leftArg.name, rightArg.name)
+                return stringsEqual(left.libraryName, right.libraryName) &&
+                    stringsEqual(left.name, right.name)
             }
 
             return false
@@ -753,11 +659,9 @@ class SimpleElmEngine {
         // If
         if (left is If) {
             if (right is If) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.condition, rightArg.condition) &&
-                    expressionsEqual(leftArg.then, rightArg.then) &&
-                    expressionsEqual(leftArg.`else`, rightArg.`else`)
+                return expressionsEqual(left.condition, right.condition) &&
+                    expressionsEqual(left.then, right.then) &&
+                    expressionsEqual(left.`else`, right.`else`)
             }
 
             return false
@@ -766,22 +670,16 @@ class SimpleElmEngine {
         // Instance
         if (left is Instance) {
             if (right is Instance) {
-                val leftArg = left
-                val rightArg = right
-                if (!qnamesEqual(leftArg.classType, rightArg.classType)) {
+                if (!qnamesEqual(left.classType, right.classType)) {
                     return false
                 }
 
-                if (
-                    leftArg.element != null &&
-                        rightArg.element != null &&
-                        leftArg.element!!.size == rightArg.element!!.size
-                ) {
-                    for (i in leftArg.element!!.indices) {
-                        val leftElement = leftArg.element!![i]
-                        val rightElement = rightArg.element!![i]
+                if (left.element.size == right.element.size) {
+                    for (i in left.element.indices) {
+                        val leftElement = left.element[i]
+                        val rightElement = right.element[i]
                         if (
-                            !stringsEqual(leftElement!!.name, rightElement!!.name) ||
+                            !stringsEqual(leftElement.name, rightElement.name) ||
                                 !expressionsEqual(leftElement.value, rightElement.value)
                         ) {
                             return false
@@ -826,11 +724,7 @@ class SimpleElmEngine {
 
         // Null
         if (left is Null) {
-            if (right is Null) {
-                return true
-            }
-
-            return false
+            return right is Null
         }
 
         // OperandRef
@@ -845,10 +739,7 @@ class SimpleElmEngine {
         // Property
         if (left is Property) {
             if (right is Property) {
-                val leftArg = left
-                val rightArg = right
-                return stringsEqual(leftArg.scope, rightArg.scope) &&
-                    stringsEqual(leftArg.path, rightArg.path)
+                return stringsEqual(left.scope, right.scope) && stringsEqual(left.path, right.path)
             }
 
             return false
@@ -857,8 +748,7 @@ class SimpleElmEngine {
         // Query
         if (left is Query) {
             if (right is Query) {
-                val leftArg = left
-                val rightArg = right
+                // TODO: Implement Query equality
             }
 
             return false
@@ -876,8 +766,7 @@ class SimpleElmEngine {
         // Repeat
         if (left is Repeat) {
             if (right is Repeat) {
-                val leftArg = left
-                val rightArg = right
+                // TODO: Implement Repeat equality
             }
 
             return false
@@ -886,8 +775,7 @@ class SimpleElmEngine {
         // Sort
         if (left is Sort) {
             if (right is Sort) {
-                val leftArg = left
-                val rightArg = right
+                // TODO: Implement Sort equality
             }
 
             return false
@@ -896,8 +784,7 @@ class SimpleElmEngine {
         // Total
         if (left is Total) {
             if (right is Total) {
-                val leftArg = left
-                val rightArg = right
+                // TODO: Implement Total equality
             }
 
             return false
@@ -906,8 +793,7 @@ class SimpleElmEngine {
         // Tuple
         if (left is Tuple) {
             if (right is Tuple) {
-                val leftArg = left
-                val rightArg = right
+                // TODO: Implement Tuple equality
             }
 
             return false
@@ -916,14 +802,10 @@ class SimpleElmEngine {
         return false
     }
 
-    fun operandsEqual(left: FunctionRef, right: FunctionRef): Boolean {
-        if (
-            left.operand != null &&
-                right.operand != null &&
-                left.operand!!.size == right.operand!!.size
-        ) {
-            for (i in left.operand!!.indices) {
-                if (!expressionsEqual(left.operand!![i], right.operand!![i])) {
+    private fun operandsEqual(left: FunctionRef, right: FunctionRef): Boolean {
+        if (left.operand.size == right.operand.size) {
+            for (i in left.operand.indices) {
+                if (!expressionsEqual(left.operand[i], right.operand[i])) {
                     return false
                 }
             }
@@ -934,14 +816,10 @@ class SimpleElmEngine {
         return false
     }
 
-    fun operandsEqual(left: BinaryExpression, right: BinaryExpression): Boolean {
-        if (
-            left.operand != null &&
-                right.operand != null &&
-                left.operand!!.size == right.operand!!.size
-        ) {
-            for (i in left.operand!!.indices) {
-                if (!expressionsEqual(left.operand!![i], right.operand!![i])) {
+    private fun operandsEqual(left: BinaryExpression, right: BinaryExpression): Boolean {
+        if (left.operand.size == right.operand.size) {
+            for (i in left.operand.indices) {
+                if (!expressionsEqual(left.operand[i], right.operand[i])) {
                     return false
                 }
             }
@@ -952,14 +830,10 @@ class SimpleElmEngine {
         return false
     }
 
-    fun operandsEqual(left: TernaryExpression, right: TernaryExpression): Boolean {
-        if (
-            left.operand != null &&
-                right.operand != null &&
-                left.operand!!.size == right.operand!!.size
-        ) {
-            for (i in left.operand!!.indices) {
-                if (!expressionsEqual(left.operand!![i], right.operand!![i])) {
+    private fun operandsEqual(left: TernaryExpression, right: TernaryExpression): Boolean {
+        if (left.operand.size == right.operand.size) {
+            for (i in left.operand.indices) {
+                if (!expressionsEqual(left.operand[i], right.operand[i])) {
                     return false
                 }
             }
@@ -970,14 +844,10 @@ class SimpleElmEngine {
         return false
     }
 
-    fun operandsEqual(left: NaryExpression, right: NaryExpression): Boolean {
-        if (
-            left.operand != null &&
-                right.operand != null &&
-                left.operand!!.size == right.operand!!.size
-        ) {
-            for (i in left.operand!!.indices) {
-                if (!expressionsEqual(left.operand!![i], right.operand!![i])) {
+    private fun operandsEqual(left: NaryExpression, right: NaryExpression): Boolean {
+        if (left.operand.size == right.operand.size) {
+            for (i in left.operand.indices) {
+                if (!expressionsEqual(left.operand[i], right.operand[i])) {
                     return false
                 }
             }
@@ -988,7 +858,10 @@ class SimpleElmEngine {
         return false
     }
 
-    fun operatorExpressionsEqual(left: OperatorExpression?, right: OperatorExpression?): Boolean {
+    private fun operatorExpressionsEqual(
+        left: OperatorExpression?,
+        right: OperatorExpression?
+    ): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -1040,10 +913,8 @@ class SimpleElmEngine {
         // Round
         if (left is Round) {
             if (right is Round) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.operand, rightArg.operand) &&
-                    expressionsEqual(leftArg.precision, rightArg.precision)
+                return expressionsEqual(left.operand, right.operand) &&
+                    expressionsEqual(left.precision, right.precision)
             }
 
             return false
@@ -1052,10 +923,8 @@ class SimpleElmEngine {
         // Combine
         if (left is Combine) {
             if (right is Combine) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.separator, rightArg.separator)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.separator, right.separator)
             }
 
             return false
@@ -1064,10 +933,8 @@ class SimpleElmEngine {
         // Split
         if (left is Split) {
             if (right is Split) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.stringToSplit, rightArg.stringToSplit) &&
-                    expressionsEqual(leftArg.separator, rightArg.separator)
+                return expressionsEqual(left.stringToSplit, right.stringToSplit) &&
+                    expressionsEqual(left.separator, right.separator)
             }
 
             return false
@@ -1076,10 +943,8 @@ class SimpleElmEngine {
         // SplitOnMatches
         if (left is SplitOnMatches) {
             if (right is SplitOnMatches) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.stringToSplit, rightArg.stringToSplit) &&
-                    expressionsEqual(leftArg.separatorPattern, rightArg.separatorPattern)
+                return expressionsEqual(left.stringToSplit, right.stringToSplit) &&
+                    expressionsEqual(left.separatorPattern, right.separatorPattern)
             }
 
             return false
@@ -1088,10 +953,8 @@ class SimpleElmEngine {
         // PositionOf
         if (left is PositionOf) {
             if (right is PositionOf) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.string, rightArg.string) &&
-                    expressionsEqual(leftArg.pattern, rightArg.pattern)
+                return expressionsEqual(left.string, right.string) &&
+                    expressionsEqual(left.pattern, right.pattern)
             }
 
             return false
@@ -1100,10 +963,8 @@ class SimpleElmEngine {
         // LastPositionOf
         if (left is LastPositionOf) {
             if (right is LastPositionOf) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.string, rightArg.string) &&
-                    expressionsEqual(leftArg.pattern, rightArg.pattern)
+                return expressionsEqual(left.string, right.string) &&
+                    expressionsEqual(left.pattern, right.pattern)
             }
 
             return false
@@ -1112,11 +973,9 @@ class SimpleElmEngine {
         // Substring
         if (left is Substring) {
             if (right is Substring) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.stringToSub, rightArg.stringToSub) &&
-                    expressionsEqual(leftArg.startIndex, rightArg.startIndex) &&
-                    expressionsEqual(leftArg.length, rightArg.length)
+                return expressionsEqual(left.stringToSub, right.stringToSub) &&
+                    expressionsEqual(left.startIndex, right.startIndex) &&
+                    expressionsEqual(left.length, right.length)
             }
 
             return false
@@ -1129,12 +988,10 @@ class SimpleElmEngine {
         // Time
         if (left is Time) {
             if (right is Time) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.hour, rightArg.hour) &&
-                    expressionsEqual(leftArg.minute, rightArg.minute) &&
-                    expressionsEqual(leftArg.second, rightArg.second) &&
-                    expressionsEqual(leftArg.millisecond, rightArg.millisecond)
+                return expressionsEqual(left.hour, right.hour) &&
+                    expressionsEqual(left.minute, right.minute) &&
+                    expressionsEqual(left.second, right.second) &&
+                    expressionsEqual(left.millisecond, right.millisecond)
             }
 
             return false
@@ -1143,11 +1000,9 @@ class SimpleElmEngine {
         // Date
         if (left is Date) {
             if (right is Date) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.year, rightArg.year) &&
-                    expressionsEqual(leftArg.month, rightArg.month) &&
-                    expressionsEqual(leftArg.day, rightArg.day)
+                return expressionsEqual(left.year, right.year) &&
+                    expressionsEqual(left.month, right.month) &&
+                    expressionsEqual(left.day, right.day)
             }
 
             return false
@@ -1156,16 +1011,14 @@ class SimpleElmEngine {
         // DateTime
         if (left is DateTime) {
             if (right is DateTime) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.year, rightArg.year) &&
-                    expressionsEqual(leftArg.month, rightArg.month) &&
-                    expressionsEqual(leftArg.day, rightArg.day) &&
-                    expressionsEqual(leftArg.hour, rightArg.hour) &&
-                    expressionsEqual(leftArg.minute, rightArg.minute) &&
-                    expressionsEqual(leftArg.second, rightArg.second) &&
-                    expressionsEqual(leftArg.millisecond, rightArg.millisecond) &&
-                    expressionsEqual(leftArg.timezoneOffset, rightArg.timezoneOffset)
+                return expressionsEqual(left.year, right.year) &&
+                    expressionsEqual(left.month, right.month) &&
+                    expressionsEqual(left.day, right.day) &&
+                    expressionsEqual(left.hour, right.hour) &&
+                    expressionsEqual(left.minute, right.minute) &&
+                    expressionsEqual(left.second, right.second) &&
+                    expressionsEqual(left.millisecond, right.millisecond) &&
+                    expressionsEqual(left.timezoneOffset, right.timezoneOffset)
             }
 
             return false
@@ -1174,10 +1027,8 @@ class SimpleElmEngine {
         // First
         if (left is First) {
             if (right is First) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    stringsEqual(leftArg.orderBy, rightArg.orderBy)
+                return expressionsEqual(left.source, right.source) &&
+                    stringsEqual(left.orderBy, right.orderBy)
             }
 
             return false
@@ -1186,10 +1037,8 @@ class SimpleElmEngine {
         // Last
         if (left is Last) {
             if (right is Last) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    stringsEqual(leftArg.orderBy, rightArg.orderBy)
+                return expressionsEqual(left.source, right.source) &&
+                    stringsEqual(left.orderBy, right.orderBy)
             }
 
             return false
@@ -1198,10 +1047,8 @@ class SimpleElmEngine {
         // IndexOf
         if (left is IndexOf) {
             if (right is IndexOf) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.element, rightArg.element)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.element, right.element)
             }
 
             return false
@@ -1210,11 +1057,9 @@ class SimpleElmEngine {
         // Slice
         if (left is Slice) {
             if (right is Slice) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.startIndex, rightArg.startIndex) &&
-                    expressionsEqual(leftArg.endIndex, rightArg.endIndex)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.startIndex, right.startIndex) &&
+                    expressionsEqual(left.endIndex, right.endIndex)
             }
 
             return false
@@ -1241,13 +1086,11 @@ class SimpleElmEngine {
         // Message
         if (left is Message) {
             if (right is Message) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.source, rightArg.source) &&
-                    expressionsEqual(leftArg.code, rightArg.code) &&
-                    expressionsEqual(leftArg.condition, rightArg.condition) &&
-                    expressionsEqual(leftArg.message, rightArg.message) &&
-                    expressionsEqual(leftArg.severity, rightArg.severity)
+                return expressionsEqual(left.source, right.source) &&
+                    expressionsEqual(left.code, right.code) &&
+                    expressionsEqual(left.condition, right.condition) &&
+                    expressionsEqual(left.message, right.message) &&
+                    expressionsEqual(left.severity, right.severity)
             }
 
             return false
@@ -1258,11 +1101,11 @@ class SimpleElmEngine {
         return true
     }
 
-    fun operandsEqual(left: UnaryExpression, right: UnaryExpression): Boolean {
+    private fun operandsEqual(left: UnaryExpression, right: UnaryExpression): Boolean {
         return expressionsEqual(left.operand, right.operand)
     }
 
-    fun unaryExpressionsEqual(left: UnaryExpression?, right: UnaryExpression?): Boolean {
+    private fun unaryExpressionsEqual(left: UnaryExpression?, right: UnaryExpression?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -1281,23 +1124,17 @@ class SimpleElmEngine {
 
         // Abs
         // As
-        if (left is As) {
-            if (right is As) {
-                val leftArg = left
-                val rightArg = right
-                return qnamesEqual(leftArg.asType, rightArg.asType) &&
-                    typeSpecifiersEqual(leftArg.asTypeSpecifier, rightArg.asTypeSpecifier) &&
-                    leftArg.isStrict() == rightArg.isStrict()
-            }
+        if (left is As && right is As) {
+            return qnamesEqual(left.asType, right.asType) &&
+                typeSpecifiersEqual(left.asTypeSpecifier, right.asTypeSpecifier) &&
+                left.isStrict() == right.isStrict()
         }
         // Ceiling
         // CanConvert
         if (left is CanConvert) {
             if (right is CanConvert) {
-                val leftArg = left
-                val rightArg = right
-                return qnamesEqual(leftArg.toType, rightArg.toType) &&
-                    typeSpecifiersEqual(leftArg.toTypeSpecifier, rightArg.toTypeSpecifier)
+                return qnamesEqual(left.toType, right.toType) &&
+                    typeSpecifiersEqual(left.toTypeSpecifier, right.toTypeSpecifier)
             }
 
             return false
@@ -1305,10 +1142,8 @@ class SimpleElmEngine {
         // Convert
         if (left is Convert) {
             if (right is Convert) {
-                val leftArg = left
-                val rightArg = right
-                return qnamesEqual(leftArg.toType, rightArg.toType) &&
-                    typeSpecifiersEqual(leftArg.toTypeSpecifier, rightArg.toTypeSpecifier)
+                return qnamesEqual(left.toType, right.toType) &&
+                    typeSpecifiersEqual(left.toTypeSpecifier, right.toTypeSpecifier)
             }
 
             return false
@@ -1340,10 +1175,8 @@ class SimpleElmEngine {
         // Is
         if (left is Is) {
             if (right is Is) {
-                val leftArg = left
-                val rightArg = right
-                return qnamesEqual(leftArg.isType, rightArg.isType) &&
-                    typeSpecifiersEqual(leftArg.isTypeSpecifier, rightArg.isTypeSpecifier)
+                return qnamesEqual(left.isType, right.isType) &&
+                    typeSpecifiersEqual(left.isTypeSpecifier, right.isTypeSpecifier)
             }
             return false
         }
@@ -1388,7 +1221,7 @@ class SimpleElmEngine {
         return true
     }
 
-    fun binaryExpressionsEqual(left: BinaryExpression?, right: BinaryExpression?): Boolean {
+    private fun binaryExpressionsEqual(left: BinaryExpression?, right: BinaryExpression?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -1462,7 +1295,10 @@ class SimpleElmEngine {
         return true
     }
 
-    fun ternaryExpressionsEqual(left: TernaryExpression?, right: TernaryExpression?): Boolean {
+    private fun ternaryExpressionsEqual(
+        left: TernaryExpression?,
+        right: TernaryExpression?
+    ): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -1483,7 +1319,7 @@ class SimpleElmEngine {
         return true
     }
 
-    fun naryExpressionsEqual(left: NaryExpression?, right: NaryExpression?): Boolean {
+    private fun naryExpressionsEqual(left: NaryExpression?, right: NaryExpression?): Boolean {
         if (left == null && right == null) {
             return true
         }
@@ -1508,7 +1344,7 @@ class SimpleElmEngine {
         return false
     }
 
-    fun aggregateExpressionsEqual(
+    private fun aggregateExpressionsEqual(
         left: AggregateExpression?,
         right: AggregateExpression?
     ): Boolean {
@@ -1529,13 +1365,9 @@ class SimpleElmEngine {
         }
 
         // Aggregate
-        if (left is Aggregate) {
-            if (right is Aggregate) {
-                val leftArg = left
-                val rightArg = right
-                return expressionsEqual(leftArg.initialValue, rightArg.initialValue) &&
-                    expressionsEqual(leftArg.iteration, rightArg.iteration)
-            }
+        if (left is Aggregate && right is Aggregate) {
+            return expressionsEqual(left.initialValue, right.initialValue) &&
+                expressionsEqual(left.iteration, right.iteration)
         }
 
         // Count
diff --git a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmClinicalVisitor.kt b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmClinicalVisitor.kt
index 3dd75ca33..273325dec 100644
--- a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmClinicalVisitor.kt
+++ b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmClinicalVisitor.kt
@@ -225,8 +225,8 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
     override fun visitRetrieve(elm: Retrieve, context: C): T {
         var result = visitFields(elm, context)
 
-        for (cfe in elm.codeFilter!!) {
-            val childResult = visitCodeFilterElement(cfe!!, context)
+        for (cfe in elm.codeFilter) {
+            val childResult = visitCodeFilterElement(cfe, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -238,8 +238,8 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
             val childResult = visitExpression(elm.context!!, context)
             result = aggregateResult(result, childResult)
         }
-        for (dfe in elm.dateFilter!!) {
-            val childResult = visitDateFilterElement(dfe!!, context)
+        for (dfe in elm.dateFilter) {
+            val childResult = visitDateFilterElement(dfe, context)
             result = aggregateResult(result, childResult)
         }
         if (elm.dateRange != null) {
@@ -252,13 +252,13 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
             result = aggregateResult(result, childResult)
         }
 
-        for (ie in elm.include!!) {
-            val childResult = visitIncludeElement(ie!!, context)
+        for (ie in elm.include) {
+            val childResult = visitIncludeElement(ie, context)
             result = aggregateResult(result, childResult)
         }
 
-        for (ofe in elm.otherFilter!!) {
-            val childResult = visitOtherFilterElement(ofe!!, context)
+        for (ofe in elm.otherFilter) {
+            val childResult = visitOtherFilterElement(ofe, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -319,8 +319,8 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
      */
     override fun visitValueSetDef(elm: ValueSetDef, context: C): T {
         var result = visitFields(elm, context)
-        for (codeSystemRef in elm.codeSystem!!) {
-            val childResult = visitCodeSystemRef(codeSystemRef!!, context)
+        for (codeSystemRef in elm.codeSystem) {
+            val childResult = visitCodeSystemRef(codeSystemRef, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -355,8 +355,8 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
     override fun visitConceptDef(elm: ConceptDef, context: C): T {
         var result = visitFields(elm, context)
 
-        for (cr in elm.code!!) {
-            val childResult = visitCodeRef(cr!!, context)
+        for (cr in elm.code) {
+            val childResult = visitCodeRef(cr, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -438,8 +438,8 @@ abstract class BaseElmClinicalVisitor<T, C> : BaseElmVisitor<T, C>(), ElmClinica
     override fun visitConcept(elm: Concept, context: C): T {
         var result = visitFields(elm, context)
 
-        for (c in elm.code!!) {
-            val childResult = visitCode(c!!, context)
+        for (c in elm.code) {
+            val childResult = visitCode(c, context)
             result = aggregateResult(result, childResult)
         }
 
diff --git a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmLibraryVisitor.kt b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmLibraryVisitor.kt
index 40afea805..90e58ad4d 100644
--- a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmLibraryVisitor.kt
+++ b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmLibraryVisitor.kt
@@ -36,47 +36,47 @@ abstract class BaseElmLibraryVisitor<T, C> :
     override fun visitLibrary(elm: Library, context: C): T {
         var result = visitFields(elm, context)
         elm.usings?.def?.forEach {
-            val childResult = visitUsingDef(it!!, context)
+            val childResult = visitUsingDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.includes?.def?.forEach {
-            val childResult = visitIncludeDef(it!!, context)
+            val childResult = visitIncludeDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.codeSystems?.def?.forEach {
-            val childResult = visitCodeSystemDef(it!!, context)
+            val childResult = visitCodeSystemDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.valueSets?.def?.forEach {
-            val childResult = visitValueSetDef(it!!, context)
+            val childResult = visitValueSetDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.codes?.def?.forEach {
-            val childResult = visitElement(it!!, context)
+            val childResult = visitElement(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.concepts?.def?.forEach {
-            val childResult = visitConceptDef(it!!, context)
+            val childResult = visitConceptDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.parameters?.def?.forEach {
-            val childResult = visitParameterDef(it!!, context)
+            val childResult = visitParameterDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.contexts?.def?.forEach {
-            val childResult = visitContextDef(it!!, context)
+            val childResult = visitContextDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
         elm.statements?.def?.forEach {
-            val childResult = visitExpressionDef(it!!, context)
+            val childResult = visitExpressionDef(it, context)
             result = aggregateResult(result, childResult)
         }
 
diff --git a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmVisitor.kt b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmVisitor.kt
index e8f44c8c6..6e199228b 100644
--- a/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmVisitor.kt
+++ b/Src/java/elm/src/main/kotlin/org/cqframework/cql/elm/visiting/BaseElmVisitor.kt
@@ -398,8 +398,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitTupleTypeSpecifier(elm: TupleTypeSpecifier, context: C): T {
         var result = defaultResult(elm, context)
 
-        for (element in elm.element!!) {
-            val childResult = visitTupleElementDefinition(element!!, context)
+        for (element in elm.element) {
+            val childResult = visitTupleElementDefinition(element, context)
             result = aggregateResult(result, childResult)
         }
         return result
@@ -416,8 +416,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitChoiceTypeSpecifier(elm: ChoiceTypeSpecifier, context: C): T {
         var result = defaultResult(elm, context)
 
-        for (choice in elm.choice!!) {
-            val childResult = visitTypeSpecifier(choice!!, context)
+        for (choice in elm.choice) {
+            val childResult = visitTypeSpecifier(choice, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -711,8 +711,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitFunctionDef(elm: FunctionDef, context: C): T {
         var result = visitFields(elm, context)
 
-        for (operand in elm.operand!!) {
-            val childResult = visitOperandDef(operand!!, context)
+        for (operand in elm.operand) {
+            val childResult = visitOperandDef(operand, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -746,13 +746,13 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitFunctionRef(elm: FunctionRef, context: C): T {
         var result = visitFields(elm, context)
 
-        for (element in elm.operand!!) {
-            val childResult = visitExpression(element!!, context)
+        for (element in elm.operand) {
+            val childResult = visitExpression(element, context)
             result = aggregateResult(result, childResult)
         }
 
-        for (s in elm.signature!!) {
-            val childResult = visitTypeSpecifier(s!!, context)
+        for (s in elm.signature) {
+            val childResult = visitTypeSpecifier(s, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -859,8 +859,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitTuple(elm: Tuple, context: C): T {
         var result = visitFields(elm, context)
 
-        for (element in elm.element!!) {
-            if (element!!.value != null) {
+        for (element in elm.element) {
+            if (element.value != null) {
                 val childResult = visitExpression(element.value!!, context)
                 result = aggregateResult(result, childResult)
             }
@@ -895,8 +895,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitInstance(elm: Instance, context: C): T {
         var result = visitFields(elm, context)
 
-        for (element in elm.element!!) {
-            if (element!!.value != null) {
+        for (element in elm.element) {
+            if (element.value != null) {
                 val childResult = visitExpression(element.value!!, context)
                 result = aggregateResult(result, childResult)
             }
@@ -965,8 +965,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
             result = aggregateResult(result, childResult)
         }
 
-        for (element in elm.element!!) {
-            val childResult = visitExpression(element!!, context)
+        for (element in elm.element) {
+            val childResult = visitExpression(element, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -1091,8 +1091,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
             result = aggregateResult(result, childResult)
         }
 
-        for (ci in elm.caseItem!!) {
-            val childResult = visitCaseItem(ci!!, context)
+        for (ci in elm.caseItem) {
+            val childResult = visitCaseItem(ci, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -2903,8 +2903,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
             val childResult = visitExpression(elm.source!!, context)
             result = aggregateResult(result, childResult)
         }
-        for (sbi in elm.by!!) {
-            val childResult = visitSortByItem(sbi!!, context)
+        for (sbi in elm.by) {
+            val childResult = visitSortByItem(sbi, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3410,8 +3410,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitSortClause(elm: SortClause, context: C): T {
         var result = visitFields(elm, context)
 
-        for (sbi in elm.by!!) {
-            val childResult = visitSortByItem(sbi!!, context)
+        for (sbi in elm.by) {
+            val childResult = visitSortByItem(sbi, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3470,17 +3470,17 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     override fun visitQuery(elm: Query, context: C): T {
         var result = visitFields(elm, context)
 
-        for (source in elm.source!!) {
-            val childResult = visitAliasedQuerySource(source!!, context)
+        for (source in elm.source) {
+            val childResult = visitAliasedQuerySource(source, context)
             result = aggregateResult(result, childResult)
         }
-        for (let in elm.let!!) {
-            val childResult = visitLetClause(let!!, context)
+        for (let in elm.let) {
+            val childResult = visitLetClause(let, context)
             result = aggregateResult(result, childResult)
         }
 
-        for (r in elm.relationship!!) {
-            val childResult = visitRelationshipClause(r!!, context)
+        for (r in elm.relationship) {
+            val childResult = visitRelationshipClause(r, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3570,8 +3570,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
             result = aggregateResult(result, childResult)
         }
 
-        for (s in elm.signature!!) {
-            val childResult = visitTypeSpecifier(s!!, context)
+        for (s in elm.signature) {
+            val childResult = visitTypeSpecifier(s, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3624,8 +3624,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     protected fun visitFields(elm: NaryExpression, context: C): T {
         var result = visitFields(elm as OperatorExpression, context)
 
-        for (e in elm.operand!!) {
-            val childResult = visitExpression(e!!, context)
+        for (e in elm.operand) {
+            val childResult = visitExpression(e, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3642,8 +3642,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     protected fun visitFields(elm: TernaryExpression, context: C): T {
         var result = visitFields(elm as OperatorExpression, context)
 
-        for (s in elm.operand!!) {
-            val childResult = visitExpression(s!!, context)
+        for (s in elm.operand) {
+            val childResult = visitExpression(s, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3660,8 +3660,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     protected fun visitFields(elm: OperatorExpression, context: C): T {
         var result = visitFields(elm as Expression, context)
 
-        for (s in elm.signature!!) {
-            val childResult = visitTypeSpecifier(s!!, context)
+        for (s in elm.signature) {
+            val childResult = visitTypeSpecifier(s, context)
             result = aggregateResult(result, childResult)
         }
 
@@ -3678,8 +3678,8 @@ abstract class BaseElmVisitor<T, C> : ElmVisitor<T, C> {
     protected open fun visitFields(elm: BinaryExpression, context: C): T {
         var result = visitFields(elm as OperatorExpression, context)
 
-        for (e in elm.operand!!) {
-            val childResult = visitExpression(e!!, context)
+        for (e in elm.operand) {
+            val childResult = visitExpression(e, context)
             result = aggregateResult(result, childResult)
         }
 
diff --git a/Src/java/model/src/main/kotlin/org/hl7/cql/model/ClassTypeElement.kt b/Src/java/model/src/main/kotlin/org/hl7/cql/model/ClassTypeElement.kt
index c0e08c0b2..b4d3070df 100644
--- a/Src/java/model/src/main/kotlin/org/hl7/cql/model/ClassTypeElement.kt
+++ b/Src/java/model/src/main/kotlin/org/hl7/cql/model/ClassTypeElement.kt
@@ -1,7 +1,5 @@
 package org.hl7.cql.model
 
-import java.util.*
-
 data class ClassTypeElement(
     val name: String,
     val type: DataType,
@@ -21,12 +19,11 @@ data class ClassTypeElement(
         this.name == that.name && type.isSuperTypeOf(that.type)
 
     override fun toString(): String {
-        return "$name:$type$%s%s%s"
-            .format(
-                Locale.US,
-                if (this.prohibited) " (prohibited)" else "",
-                if (this.oneBased) " (one-based)" else "",
-                if (this.target != null) " (target: " + this.target + ")" else ""
-            )
+        return """$name:$type
+            |${if (this.prohibited) " (prohibited)" else ""}
+            |${if (this.oneBased) " (one-based)" else ""}
+            |${if (this.target != null) " (target: " + this.target + ")" else ""}"""
+            .trimMargin()
+            .replace("\n", "")
     }
 }
diff --git a/Src/java/model/src/main/kotlin/org/hl7/cql/model/NamespaceManager.kt b/Src/java/model/src/main/kotlin/org/hl7/cql/model/NamespaceManager.kt
index 676539a9a..d9a78d02d 100644
--- a/Src/java/model/src/main/kotlin/org/hl7/cql/model/NamespaceManager.kt
+++ b/Src/java/model/src/main/kotlin/org/hl7/cql/model/NamespaceManager.kt
@@ -20,7 +20,7 @@ class NamespaceManager {
         addNamespace(namespaceInfo.name, namespaceInfo.uri)
     }
 
-    fun addNamespace(namespaceName: String, namespaceUri: String) {
+    private fun addNamespace(namespaceName: String, namespaceUri: String) {
         require(namespaceName.isNotEmpty()) { "namespaceName is required" }
         require(namespaceUri.isNotEmpty()) { "namespaceUri is required" }
         check(!namespaces.containsKey(namespaceName)) {
diff --git a/Src/java/model/src/main/kotlin/org/hl7/cql/model/TupleTypeElement.kt b/Src/java/model/src/main/kotlin/org/hl7/cql/model/TupleTypeElement.kt
index aee2da51d..546e6b0bd 100644
--- a/Src/java/model/src/main/kotlin/org/hl7/cql/model/TupleTypeElement.kt
+++ b/Src/java/model/src/main/kotlin/org/hl7/cql/model/TupleTypeElement.kt
@@ -15,7 +15,7 @@ data class TupleTypeElement(
     fun isSuperTypeOf(that: TupleTypeElement): Boolean =
         this.name == that.name && type.isSuperTypeOf(that.type)
 
-    override fun toString(): String = "${name}:${type}"
+    override fun toString(): String = "$name:$type"
 
-    fun toLabel(): String = "${name}: ${type}"
+    fun toLabel(): String = "$name: $type"
 }