2 files changed, 25 insertions, 1 deletions
diff --git a/tvix/eval/src/chunk.rs b/tvix/eval/src/chunk.rs
index 35fd7e78e674..04b58bde20fd 100644
--- a/tvix/eval/src/chunk.rs
+++ b/tvix/eval/src/chunk.rs
@@ -143,7 +143,15 @@ impl Chunk {
         }
 
         match self[idx] {
-            OpCode::OpConstant(idx) => writeln!(writer, "OpConstant({}@{})", self[idx], idx.0),
+            OpCode::OpConstant(idx) => {
+                let val_str = match &self[idx] {
+                    Value::Thunk(t) => t.debug_repr(),
+                    Value::Closure(c) => format!("closure({:p})", c.lambda),
+                    val => format!("{}", val),
+                };
+
+                writeln!(writer, "OpConstant({}@{})", val_str, idx.0)
+            }
             op => writeln!(writer, "{:?}", op),
         }?;
 
diff --git a/tvix/eval/src/value/thunk.rs b/tvix/eval/src/value/thunk.rs
index e30d58e72849..747cd413e23e 100644
--- a/tvix/eval/src/value/thunk.rs
+++ b/tvix/eval/src/value/thunk.rs
@@ -73,6 +73,17 @@ enum ThunkRepr {
     Evaluated(Value),
 }
 
+impl ThunkRepr {
+    fn debug_repr(&self) -> String {
+        match self {
+            ThunkRepr::Evaluated(v) => format!("thunk(val|{})", v),
+            ThunkRepr::Blackhole => "thunk(blackhole)".to_string(),
+            ThunkRepr::Native(_) => "thunk(native)".to_string(),
+            ThunkRepr::Suspended { lambda, .. } => format!("thunk({:p})", *lambda),
+        }
+    }
+}
+
 /// A thunk is created for any value which requires non-strict
 /// evaluation due to self-reference or lazy semantics (or both).
 /// Every reference cycle involving `Value`s will contain at least
@@ -428,6 +439,11 @@ impl Thunk {
             _ => false,
         }
     }
+
+    /// Helper function to format thunks in observer output.
+    pub(crate) fn debug_repr(&self) -> String {
+        self.0.borrow().debug_repr()
+    }
 }
 
 impl TotalDisplay for Thunk {