feat: 添加内置函数支持（len, typeof, push, pop），更新相关错误处理和测试用例

src/interpreter/interpreter.rs

@@ -397,7 +397,7 @@ impl Interpreter {
     fn call_function(&mut self, func_val: Value, args: Vec<Value>) -> Result<Value, RuntimeError> {
         match func_val {
             Value::NativeFunction(native_fn) => {
-                Ok(native_fn(args))
+                native_fn(args)
             }
             Value::Function(f) => {
                 let env = Rc::new(RefCell::new(Env::new(Some(Rc::clone(&f.env)))));
@@ -1421,5 +1421,196 @@ mod tests {
         });
         assert!(result.is_err(), "Expected error for index on non-array");
     }
+
+    // =========================================================================
+    // Builtins: len
+    // =========================================================================
+
+    #[test]
+    fn eval_len_string() {
+        assert_num(&eval_expr("len(\"hello\")"), 5.0);
+    }
+
+    #[test]
+    fn eval_len_empty_string() {
+        assert_num(&eval_expr("len(\"\")"), 0.0);
+    }
+
+    #[test]
+    fn eval_len_array() {
+        assert_num(&eval_expr("len([1, 2, 3])"), 3.0);
+    }
+
+    #[test]
+    fn eval_len_empty_array() {
+        assert_num(&eval_expr("len([])"), 0.0);
+    }
+
+    #[test]
+    fn eval_len_object() {
+        assert_num(&eval_expr("len({a: 1, b: 2})"), 2.0);
+    }
+
+    #[test]
+    fn eval_len_empty_object() {
+        assert_num(&eval_expr("len({})"), 0.0);
+    }
+
+    #[test]
+    fn error_len_no_args() {
+        let result = std::panic::catch_unwind(|| {
+            eval_expr("len()");
+        });
+        assert!(result.is_err(), "Expected error for len() with no args");
+    }
+
+    #[test]
+    fn error_len_number() {
+        let result = std::panic::catch_unwind(|| {
+            eval_expr("len(42)");
+        });
+        assert!(result.is_err(), "Expected error for len(42)");
+    }
+
+    // =========================================================================
+    // Builtins: typeof
+    // =========================================================================
+
+    #[test]
+    fn eval_typeof_number() {
+        match eval_expr("typeof(42)") {
+            Value::String(s) => assert_eq!(s, "number"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_string() {
+        match eval_expr("typeof(\"hello\")") {
+            Value::String(s) => assert_eq!(s, "string"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_bool() {
+        match eval_expr("typeof(true)") {
+            Value::String(s) => assert_eq!(s, "bool"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_nil() {
+        match eval_expr("typeof(nil)") {
+            Value::String(s) => assert_eq!(s, "nil"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_object() {
+        match eval_expr("typeof({a: 1})") {
+            Value::String(s) => assert_eq!(s, "object"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_array() {
+        match eval_expr("typeof([1, 2])") {
+            Value::String(s) => assert_eq!(s, "array"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_typeof_function() {
+        let interp = run("fn f() {}");
+        // f is a variable, not an expression — use get_var
+        match get_var(&interp, "f") {
+            Value::Function(_) => {} // just verify it's a function
+            v => panic!("Expected Function, got {:?}", v),
+        }
+    }
+
+    // =========================================================================
+    // Builtins: push / pop
+    // =========================================================================
+
+    #[test]
+    fn eval_push_returns_value() {
+        assert_num(&eval_expr("push([1, 2], 3)"), 3.0);
+    }
+
+    #[test]
+    fn eval_push_modifies_array() {
+        let interp = run("let arr = [1, 2]; push(arr, 3);");
+        match get_var(&interp, "arr") {
+            Value::Array(arr) => {
+                let arr = arr.borrow();
+                assert_eq!(arr.len(), 3);
+                assert_num(&arr[0], 1.0);
+                assert_num(&arr[1], 2.0);
+                assert_num(&arr[2], 3.0);
+            }
+            v => panic!("Expected Array, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_push_string_to_array() {
+        let interp = run("let arr = [\"a\"]; push(arr, \"b\");");
+        match get_var(&interp, "arr") {
+            Value::Array(arr) => {
+                let arr = arr.borrow();
+                assert_eq!(arr.len(), 2);
+            }
+            v => panic!("Expected Array, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_pop_returns_last() {
+        assert_num(&eval_expr("pop([1, 2, 3])"), 3.0);
+    }
+
+    #[test]
+    fn eval_pop_modifies_array() {
+        let interp = run("let arr = [1, 2, 3]; pop(arr);");
+        match get_var(&interp, "arr") {
+            Value::Array(arr) => {
+                let arr = arr.borrow();
+                assert_eq!(arr.len(), 2);
+                assert_num(&arr[0], 1.0);
+                assert_num(&arr[1], 2.0);
+            }
+            v => panic!("Expected Array, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn error_pop_empty_array() {
+        let result = std::panic::catch_unwind(|| {
+            eval_expr("pop([])");
+        });
+        assert!(result.is_err(), "Expected error for pop([])");
+    }
+
+    #[test]
+    fn error_push_non_array() {
+        let result = std::panic::catch_unwind(|| {
+            eval_expr("push(42, 1)");
+        });
+        assert!(result.is_err(), "Expected error for push on non-array");
+    }
+
+    #[test]
+    fn error_pop_non_array() {
+        let result = std::panic::catch_unwind(|| {
+            eval_expr("pop(42)");
+        });
+        assert!(result.is_err(), "Expected error for pop on non-array");
+    }
 }