diff --git a/runtime/ast/parser.py b/runtime/ast/parser.py
index 039391c..dd13cbe 100644
--- a/runtime/ast/parser.py
+++ b/runtime/ast/parser.py
@@ -55,7 +55,15 @@ class Parser:
             "body": body,
         }
 
+    def if_statement(self):
+        self.eat('if')
+        return {
+            "type": 'IfStatement',
+        }
+
     def expression_statement(self):
+        if self.token_type() == "if":
+            return self.if_statement()
         if self.token_type() == "return":
             return self.return_statement()
         if self._is_literal():
diff --git a/runtime/ast/runtime.py b/runtime/ast/runtime.py
index a000724..901f666 100644
--- a/runtime/ast/runtime.py
+++ b/runtime/ast/runtime.py
@@ -32,9 +32,8 @@ class Runtime:
     def assignment_expression(self, ast):
         id = ast.get("identifier").get("name")
         v = ast.get("value")
-        l = self.literal(v)
-        self.records[id] = self.unquote(v)
-        
+        self.set_identifier_value(id, self.unquote(v))
+    
     def _is_call_function(self, ast):
         return ast["type"] == "CallExpression"
 
@@ -44,14 +43,32 @@ class Runtime:
         unquoted_args = []
         for arg in args:
             unquoted_args.append(self.unquote(arg))
-        fu = self.records.get(id)
+        fu = self.get_identifier_value(id)
         if fu == None:
             raise Exception("Function not found: " + id)
         return fu(*unquoted_args)
+    
+    def get_identifier_value(self, key):
+        v = self.records.get(key)
+        if v != None:
+            return v
+        if self.parent != None:
+            return self.parent.get_identifier_value(key)
+        return None
+
+    def set_identifier_value(self, key, value):
+        v = self.records.get(key)
+        if v != None:
+            self.records[key] = value
+            return
+        if self.parent != None:
+            self.parent.set_identifier_value(key, value)
+            return
+        raise Exception("Identifier not found: " + key)
 
     def unquote(self, ast):
         if self._is_identifier(ast):
-            return self.records.get(ast.get("name"))
+            return self.get_identifier_value(ast.get("name"))
         if self._is_literal(ast):
             return self.literal(ast)
         if self._is_call_function(ast):
diff --git a/runtime/ast/tokenizer.py b/runtime/ast/tokenizer.py
index 1a1467f..4071b3b 100644
--- a/runtime/ast/tokenizer.py
+++ b/runtime/ast/tokenizer.py
@@ -39,6 +39,15 @@ specs = (
     # Assignment:
     (re.compile(r"^="), "SIMPLE_ASSIGN"),
 
+    # Logical operators:
+    (re.compile(r"^&&"), "AND"),
+    (re.compile(r"^\|\|"), "OR"),
+    (re.compile(r"^!"), "NOT"),
+
+    # Math operators: +, -, *, /:
+    (re.compile(r"^[+-]"), "ADDITIVE_OPERATOR"),
+    (re.compile(r"^[*/]"), "MULTIPLICATIVE_OPERATOR"),
+
     # Double-quoted strings
     (re.compile(r"^\"[^\"]*\""), "STRING"),
 
diff --git a/runtime_example.py b/runtime_example.py
index 427f159..b12a6f5 100644
--- a/runtime_example.py
+++ b/runtime_example.py
@@ -4,10 +4,9 @@ from runtime.ast.parser import Parser
 from runtime.ast.runtime import Runtime
 
 script = """
-let hello = true
-let text = audio_to_text(audio)
-print(hello)
-return tts(text)
+let hello = add(div(1,2),2)
+
+return hello
 """
 
 def version():
@@ -42,10 +41,7 @@ if __name__ == "__main__":
         "version": version,
         "print": print
     })
+    ast = Parser().parse(script)
     # 注入數據
-    script_output = runtime.run(Parser().parse(script), {
-        "audio": audio_data
-    })
-    f = open("./test_data/runtime_output.mp3", "wb")
-    f.write(script_output.read())
-    f.close()
\ No newline at end of file
+    script_output = runtime.run(ast, {})
+    print("script:",script_output)
\ No newline at end of file