Before you had to write:

  function is_not_numeric($num){
    !is_numeric($num);
  }

  array_map('is_not_numeric', array(1,3,5,'a','c',3));

The fact that php used to take a string as the callback and not an expression is seriously broken.

Now (presumably), one can write:

  array_map(function($x){ !is_numeric($x) }, array(1,3,5,'a','c',3));

Although, ideally it would be:

  array_map(!is_numeric, array(1,3,5,'a','c',3));