php to reverse a string without using loops or builtin functions

Question

How would you write a short php function to reverse a string. The function must:

• have only one argument
• not use the built-in function 'strrev' or 'array_reverse'
• not a use a looping construct like 'for', 'foreach' or 'while'.

Answer 1

Quickly scanning down, these all look so long!

function rev($str) {
    return $str?rev(substr($str,1)).$str[0]:'';
}

Recursive so obviously doesn't work on strings longer than 100 chars.