code: public function visitCallableType(CallableType $type)
      {
          $this->typeCheck->visitCallableType(func_get_args());
  
          $call = new Call(QualifiedIdentifier::fromString('\is_callable'));
          $call->add($this->valueExpression());
  
          return $call;
      }
docs: @param CallableType $type
  
  @return Call