Adjust paranthesis handling

src/zfitwrapper/ModelParser.py

@@ -93,15 +93,16 @@ class ModelParser:
 
         return expression
 
-    def _lexical_analysis(self) -> List[Node]:
-        token_pattern = r"(\w+@\w+|\w+|[+*()@])"
-        tokens = re.findall(token_pattern, self.modelstring)
+    def _lexical_analysis(self, input_string: str) -> List[Node]:
+        token_pattern = r"(\w+@\w+|\w+@\([^\)]+\)|\w+|[+*()])"
+        tokens = re.findall(token_pattern, input_string)
 
         for expr in tokens:
-            if re.match(r"\w+@\w+", expr):
+            if re.match(r"\w+@(\w+|\()", expr):
                 param_name, model_name = expr.split("@")
                 token = Node(TokenType.T_EXT, value=model_name, ext_param=param_name)
                 self._nodeTokens.append(token)
+
             elif re.match(r"\w+", expr):
                 token = Node(TokenType.T_MODEL, value=expr)
                 self._nodeTokens.append(token)
@@ -114,12 +115,12 @@ class ModelParser:
             else:
                 raise Exception("Invalid token: {}".format(expr))
 
-        self._nodeTokens.append(Node(TokenType.T_END))
-
         return self._nodeTokens
 
     def parse(self) -> Node:
-        tokens = self._lexical_analysis()
+        tokens = self._lexical_analysis(self.modelstring)
+        self._nodeTokens.append(Node(TokenType.T_END))
+
         fNode = self.__baseParse(tokens)
         self.__match(tokens, TokenType.T_END)