title: php to reverse a string without using loops or builtin functions
body: <p>How would you write a short php function to reverse a string. The function must: </p>
  
  <ul>
  <li>have only one argument</li>
  <li>not use the built-in function 'strrev' or 'array_reverse'</li>
  <li>not a use a looping construct like 'for', 'foreach' or 'while'.</li>
  </ul>