fix factorial example

src/eval/deep_eval.ts

@@ -107,19 +107,21 @@ export function deepEvalCall(s: CallBlockState, env: DynamicEnvironment): DeepEv
   }
 }
 export function deepEvalLet(s: LetInBlockState, env: DynamicEnvironment): DeepEvalResultLet {
+  let valueResult;
   const valueEnv = {
     names: trie.insert(env.names)(s.name)({
+      // dirty: we introduce indirection to enable recursion
       recursive: true,
       i: () => {
         try {
-          return { val: valueResult.val };
+          return valueResult;
         } catch (e) {
           return { err: e };
         }
       },
     }),
   };
-  const valueResult = deepEvalExpr(s.value, valueEnv);
+  valueResult = deepEvalExpr(s.value, valueEnv);
   const innerEnv = {
     names: trie.insert(env.names)(s.name)({i: valueResult.val}),
   }