Check corresponding blog post at http://spiechu.pl/2014/02/09/playing-with-php-functional-way

string_converter.php

<?php

$standardTasks = [
  // nothing special here, take $val and return trimmed
  'standardTrim' => function($val) {
    return trim($val);
  },
  
  // this one is better, check string encoding and convert to ASCII counterpart
  'convertToASCII' => function($val) {
    $encoding = mb_detect_encoding($val);
    return ($encoding === 'ASCII') ? $val : iconv($encoding, 'ASCII//TRANSLIT', $val);
  },
  
  // this function cannot be applied to $val directly,
  // firstly you need to call function with $char which will
  // expose closure function to work with
  'eliminateChar' => function($char) {
    return function ($val) use ($char) {
      return str_replace($char, '', $val);
    };
  },
  
  // same trick, but this time creates an array as result
  'splitByChar' => function($char) {
    return function($val) use ($char) {
      return explode($char, $val);
    };
  },
];

// suppose we have string on which we need to perform following tasks:
$jobsToDo = [
    $standardTasks['convertToASCII'],
    $standardTasks['splitByChar']('|'),
    $standardTasks['eliminateChar'](','),
    $standardTasks['standardTrim'],
];

// string to process
$strToParse = 'Ala ma kota |Używałem GG jak byłem mały, a teraz już nie ';

// do not modify original string
$result = $strToParse;

// `use` keyword allows us to see the variable from inside anonymous function
// `&` sign passes $result as reference
array_walk($jobsToDo, function(callable $val) use (&$result) {
    // 'splitByChar' creates array,
    // so we need to apply task on every array value
    $result = is_array($result) ? array_map($val, $result) : $val($result);
});

// The result is as expected:
// array [
//   0 => string 'Ala ma kota'
//   1 => string 'Uzywalem GG jak bylem maly a teraz juz nie'
// ]