Condition function for is parent category?

I’m not sure I fully understood your question, but wrapping a function inside a new function will make it shorter. For example, do the following in your functions.php file:

function is_parent($slug){
   if(is_category($slug)){
       return true;
   }else{
       return false;
   }
}

And then simply use it like:

if(is_parent('slug')){
    // do something
}