From e97abba2539e450eb028c20ae68529a2af3eb25f Mon Sep 17 00:00:00 2001
From: "Jonathan D.A. Jewell" <6759885+hyperpolymath@users.noreply.github.com>
Date: Mon, 11 May 2026 05:33:28 +0200
Subject: [PATCH] fix(codegen): resolve top-level const refs in ExprVar (#73)

ExprVar name lookup fell through to UnboundVariable after checking
locals and variant_tags, never reaching func_indices where TopConst
bindings are stored (negative sentinel: global_idx = -(k+1)).
Add a GlobalGet fallback so const identifiers used inside fn bodies
compile correctly.

check already passed; compile now passes too.
---
 lib/codegen.ml | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/codegen.ml b/lib/codegen.ml
index 0863a04..9e6534a 100644
--- a/lib/codegen.ml
+++ b/lib/codegen.ml
@@ -436,7 +436,13 @@ let rec gen_expr (ctx : context) (expr : expr) : (context * instr list) result =
            UnboundVariable even though the parser accepts it. *)
         begin match List.assoc_opt id.name ctx.variant_tags with
           | Some tag -> Ok (ctx, [I32Const (Int32.of_int tag)])
-          | None -> Error (UnboundVariable id.name)
+          | None ->
+            (* Top-level const bindings are stored in func_indices with a
+               negative sentinel: actual global index = -(k+1). *)
+            begin match List.assoc_opt id.name ctx.func_indices with
+              | Some k when k < 0 -> Ok (ctx, [GlobalGet (-(k + 1))])
+              | _ -> Error (UnboundVariable id.name)
+            end
         end
     end