hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
hash_expr env (Case e _ _ _) = hash_expr env e
hash_expr env (Lam b e) = hash_expr (extend_env env b) e
hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
hash_expr env (Case e _ _ _) = hash_expr env e
hash_expr env (Lam b e) = hash_expr (extend_env env b) e