better error handling

src/eval/eval.ts

@@ -60,7 +60,7 @@ export function evalLet(s: LetInBlockState, env: DynamicEnvironment): EvalResult
   const valueEnv = {
     names: trie.insert(env.names)(s.name)({
       recursive: true,
-      i: () => value,
+      i: () => { try { return value; } catch (e) {} },
     }),
   };
   const value = evalExpr(s.value, valueEnv);