code: def call(self):
          
          is_mutable = False
          if self.token.nature == Nature.MUT:
              is_mutable = True
              self._process(Nature.MUT)
  
          identifier = Identifier(name=self.token.value)
          self._process(Nature.ID)
  
          if self.token.nature == Nature.LPAREN:
              return FunctionCall(identifier=identifier, parameters=self.parameters())
          else:
              return Variable(identifier=identifier, is_mutable=is_mutable)
docs: call: ['mut'] ID ['(' parameters ')']