Rewritten debugVar with a custom reifier

klogic-core/src/main/kotlin/org/klogic/core/Goal.kt

@@ -53,10 +53,10 @@ fun delay(f: () -> Goal): Goal = { st: State -> ThunkStream { f()(st) } }
 /**
  * Reifies walked [term] using the passed [reifier] and returns a Goal from the passed [callBack].
  */
-fun <T : Term<T>> debugVar(
+fun <T : Term<T>, Reified : ReifiedTerm<*>> debugVar(
     term: Term<T>,
-    reifier: (Term<T>) -> ReifiedTerm<T>,
-    callBack: (ReifiedTerm<T>) -> Goal
+    reifier: (Term<T>) -> Reified,
+    callBack: (Reified) -> Goal
 ): Goal = { st: State ->
     val walkedTerm = term.walk(st.substitution)
     val reified = reifier(walkedTerm)

klogic-core/src/test/kotlin/org/klogic/core/ReifyTest.kt

@@ -0,0 +1,21 @@
+package org.klogic.core
+
+import org.junit.jupiter.api.Test
+import org.klogic.utils.terms.PeanoLogicNumber
+import org.klogic.utils.terms.PeanoLogicNumber.Companion.succ
+import org.klogic.utils.terms.ZeroNaturalNumber.Z
+
+class ReifyTest {
+    @Test
+    fun testDebugVar() {
+        // TODO test plus here.
+    }
+
+    // TODO rewrite using debugVar.
+    private fun plus(x: Term<PeanoLogicNumber>, y: Term<PeanoLogicNumber>, z: Term<PeanoLogicNumber>): Goal = conde(
+        (x `===` Z) and (z `===` y),
+        freshTypedVars<PeanoLogicNumber, PeanoLogicNumber> { a, b ->
+            (x `===` succ(a)) and (z `===` succ(b)) and plus(a, y, b)
+        }
+    )
+}