Fix variable shadowing

Author: saulshanabrook

docs/changelog.md

@@ -7,7 +7,7 @@ _This project uses semantic versioning_
 - Upgrade egglog which includes new backend.
   - Fixes implementation of the Python Object sort to work with objects with dupliating hashes but the same value.
     Also changes the representation to be an index into a list instead of the ID, making egglog programs more deterministic.
-  - Prefix constant declerations to not shadow local variables
+  - Prefix constant declerations and unbound variables to not shadow let variables
   - BREAKING: Remove `simplify` since it was removed upstream. You can manually replace it with an insert, run, then extract.
 
 ## 10.0.2 (2025-06-22)

python/egglog/egraph_state.py

@@ -406,7 +406,8 @@ def _expr_to_egg(self, expr_decl: ExprDecl) -> bindings._Expr:  # noqa: PLR0912,
             case LetRefDecl(name):
                 res = bindings.Var(span(), f"{name}")
             case UnboundVarDecl(name):
-                res = bindings.Var(span(), name)
+                # Prefix vars with an _ to avoid name conflicts
+                res = bindings.Var(span(), f"_{name}")
             case LitDecl(value):
                 l: bindings._Literal
                 match value:

python/tests/test_unstable_fn.py

@@ -315,10 +315,6 @@ def apply_f(f: Callable[[A], A], x: A) -> A:
         egraph = EGraph(save_egglog_string=True)
         x = egraph.let("x", apply_f(lambda x: A(), A()))
         y = egraph.let("y", apply_f(lambda x: alt_a, A()))
-        print(egraph.run(10))
-        print(egraph.extract(x))
-        print(egraph.as_egglog_string)
-        egraph.display(n_inline_leaves=0)
         egraph.check(eq(x).to(A()))
         egraph.check(eq(y).to(alt_a))