How to use anonymous functions for simple filters

0.php

<?php
/**
 * This gist is example code that goes with an article on how (and why/when) to use
 * PHP anonymous functions. To view the entire post, go to:
 * https://rocketgeek.com/basics/using-anonymous-functions-for-filters-and-actions/
 */

1.php

add_filter( 'name_of_hook', 'name_of_function_to_use' );

2.php

function name_of_function_called( $some_argument ) {
  // do something...
  return $something;
} 

3.php

add_filter( 'excerpt_length', 'excerpt_length_example' );
function excerpt_length_example( $words ) {
  return 15;
}

4.php

add_filter( 'excerpt_length', function( $words ) {
  return 15;
});