diff --git a/ergotree-interpreter/src/eval/deserialize_context.rs b/ergotree-interpreter/src/eval/deserialize_context.rs
index cbb88fcd2..49485e389 100644
--- a/ergotree-interpreter/src/eval/deserialize_context.rs
+++ b/ergotree-interpreter/src/eval/deserialize_context.rs
@@ -14,8 +14,12 @@ impl Evaluable for DeserializeContext {
     fn eval(&self, env: &mut Env, ctx: &mut EvalContext) -> Result<Value, EvalError> {
         match ctx.ctx.extension.values.get(&self.id) {
             Some(c) => {
-                if c.tpe != SType::SColl(SType::SByte.into()) {
-                    Err(EvalError::UnexpectedExpr(format!("DeserializeContext: expected extension value to have type SColl(SByte), got {:?}", c.tpe)))
+                let expected_tpe = SType::SColl(SType::SByte.into());
+                if c.tpe != expected_tpe {
+                    Err(EvalError::UnexpectedExpr(format!(
+                        "DeserializeContext: expected extension value to have type {:?} got {:?}",
+                        expected_tpe, c.tpe
+                    )))
                 } else {
                     let bytes = c.v.clone().try_extract_into::<Vec<u8>>()?;
                     let expr = Expr::sigma_parse_bytes(bytes.as_slice())?;
@@ -26,8 +30,8 @@ impl Evaluable for DeserializeContext {
                 }
             }
             None => Err(EvalError::NotFound(format!(
-                "DeserializeContext: no value with id {} in context extension",
-                self.id
+                "DeserializeContext: no value with id {} in context extension map {}",
+                self.id, ctx.ctx.extension
             ))),
         }
     }
diff --git a/ergotree-interpreter/src/eval/expr.rs b/ergotree-interpreter/src/eval/expr.rs
index 2c04f17a4..651999dd5 100644
--- a/ergotree-interpreter/src/eval/expr.rs
+++ b/ergotree-interpreter/src/eval/expr.rs
@@ -40,7 +40,7 @@ impl Evaluable for Expr {
             )),
             Expr::Collection(op) => op.eval(env, ctx),
             Expr::ValDef(_) => Err(EvalError::UnexpectedExpr(
-                ("ValDef is evaluated in BlockValue").to_string(),
+                ("ValDef should be evaluated in BlockValue").to_string(),
             )),
             Expr::And(op) => op.eval(env, ctx),
             Expr::Or(op) => op.eval(env, ctx),
diff --git a/ergotree-interpreter/src/eval/get_var.rs b/ergotree-interpreter/src/eval/get_var.rs
index 07bbbfb7c..1ac5e34e6 100644
--- a/ergotree-interpreter/src/eval/get_var.rs
+++ b/ergotree-interpreter/src/eval/get_var.rs
@@ -1,4 +1,3 @@
-// use ergotree_ir::mir::constant::TryExtractInto;
 use ergotree_ir::mir::constant::TryExtractFromError;
 use ergotree_ir::mir::get_var::GetVar;
 use ergotree_ir::mir::value::Value;
@@ -14,8 +13,8 @@ impl Evaluable for GetVar {
             None => Ok(Value::Opt(None.into())),
             Some(v) if v.tpe == self.var_tpe => Ok((Some(v.v.clone())).into()),
             Some(v) => Err(TryExtractFromError(format!(
-                "GetVar: expected {:?}, found {:?}",
-                self.var_tpe, v.tpe
+                "GetVar: expected extension value id {} to have type {:?}, found {:?} in context extension map {}",
+                self.var_id, self.var_tpe, v, ctx.ctx.extension
             ))
             .into()),
         }
diff --git a/ergotree-interpreter/src/sigma_protocol/prover/context_extension.rs b/ergotree-interpreter/src/sigma_protocol/prover/context_extension.rs
index 09aed3e41..ed245147f 100644
--- a/ergotree-interpreter/src/sigma_protocol/prover/context_extension.rs
+++ b/ergotree-interpreter/src/sigma_protocol/prover/context_extension.rs
@@ -7,6 +7,7 @@ use ergotree_ir::serialization::SigmaSerializable;
 use ergotree_ir::serialization::SigmaSerializeResult;
 use indexmap::IndexMap;
 use std::convert::TryFrom;
+use std::fmt;
 use thiserror::Error;
 
 /// User-defined variables to be put into context
@@ -25,6 +26,12 @@ impl ContextExtension {
     }
 }
 
+impl fmt::Display for ContextExtension {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_map().entries(self.values.iter()).finish()
+    }
+}
+
 impl SigmaSerializable for ContextExtension {
     fn sigma_serialize<W: SigmaByteWrite>(&self, w: &mut W) -> SigmaSerializeResult {
         w.put_u8(self.values.len() as u8)?;
diff --git a/ergotree-ir/src/mir/constant.rs b/ergotree-ir/src/mir/constant.rs
index e3ff14b09..be58514c0 100644
--- a/ergotree-ir/src/mir/constant.rs
+++ b/ergotree-ir/src/mir/constant.rs
@@ -88,6 +88,12 @@ impl std::fmt::Debug for Constant {
     }
 }
 
+impl std::fmt::Display for Constant {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        self.v.fmt(f)
+    }
+}
+
 impl std::fmt::Debug for Literal {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         match self {
@@ -112,6 +118,63 @@ impl std::fmt::Debug for Literal {
     }
 }
 
+impl std::fmt::Display for Literal {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Literal::Coll(CollKind::NativeColl(NativeColl::CollByte(i8_bytes))) => {
+                write!(f, "Coll[Byte](");
+                for (i, b) in i8_bytes.iter().enumerate() {
+                    if i > 0 {
+                        write!(f, ", ")?;
+                    }
+                    write!(f, "{}", b)?;
+                }
+                write!(f, ")")
+            }
+            Literal::Coll(CollKind::WrappedColl { elem_tpe, items }) => {
+                write!(f, "Coll[{}](", elem_tpe)?;
+                for (i, item) in items.iter().enumerate() {
+                    if i > 0 {
+                        write!(f, ", ")?;
+                    }
+                    item.fmt(f)?;
+                }
+                write!(f, ")")
+            }
+            Literal::Opt(boxed_opt) => {
+                if let Some(v) = &**boxed_opt {
+                    write!(f, "Some(")?;
+                    v.fmt(f)?;
+                    write!(f, ")")
+                } else {
+                    write!(f, "None")
+                }
+            }
+            Literal::Tup(items) => {
+                write!(f, "(")?;
+                for (i, item) in items.iter().enumerate() {
+                    if i > 0 {
+                        write!(f, ", ")?;
+                    }
+                    item.fmt(f)?;
+                }
+                write!(f, ")")
+            }
+            Literal::Unit => write!(f, "()"),
+            Literal::Boolean(v) => v.fmt(f),
+            Literal::Byte(v) => v.fmt(f),
+            Literal::Short(v) => v.fmt(f),
+            Literal::Int(v) => v.fmt(f),
+            Literal::Long(v) => write!(f, "{}L", v),
+            Literal::BigInt(v) => v.fmt(f),
+            Literal::SigmaProp(v) => v.fmt(f),
+            Literal::GroupElement(v) => v.fmt(f),
+            Literal::AvlTree(v) => v.fmt(f),
+            Literal::CBox(v) => v.fmt(f),
+        }
+    }
+}
+
 impl From<()> for Literal {
     fn from(_: ()) -> Literal {
         Literal::Unit