Bug fix: get_tree when using no parameter functions

当调用无参数的函数是，其parameters会成为None，导致调用get_tree函数报错，添加一个判断即可解决问题

Author: iewnfod

src/AST/function.py

@@ -13,7 +13,10 @@ def __init__(self, id, parameters, statements, returns=None, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     def get_tree(self, level=0):
-        return LEVEL_STR * level + self.type + ' ' + str(self.id) + '\n' + self.parameters.get_tree(level+1) + '\n' + self.statements.get_tree(level+1)
+        if self.parameters:
+            return LEVEL_STR * level + self.type + ' ' + str(self.id) + '\n' + self.parameters.get_tree(level+1) + '\n' + self.statements.get_tree(level+1)
+        else:
+            return LEVEL_STR * level + self.type + ' ' + str(self.id) + '\n' + self.statements.get_tree(level+1)
 
     def exe(self):
         stack.add_function(self)
@@ -26,7 +29,10 @@ def __init__(self, id, parameters=None, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     def get_tree(self, level=0):
-        return LEVEL_STR * level + self.type + ' ' + str(self.id) + '\n' + self.parameters.get_tree(level+1)
+        if self.parameters:
+            return LEVEL_STR * level + self.type + ' ' + str(self.id) + '\n' + self.parameters.get_tree(level+1)
+        else:
+            return LEVEL_STR * level + self.type + ' ' + str(self.id)
 
     def exe(self):
         new_dict = {}  # {变量名: (值, 类型, 是否是常量)}

test/test.cpc

@@ -1,3 +1,5 @@
-DECLARE a : INTEGER
-a <- 1
-OUTPUT a
+FUNCTION a RETURNS INTEGER
+	RETURN 1
+ENDFUNCTION
+
+OUTPUT 1