php function composition compose

php-compose.php

function compose() {
    $fxns = func_get_args();
    $outer = function($identity) { return $identity; };
    while($f = array_pop($fxns)) {
        if ( !is_callable($f) ) {
            throw new \Exception('This should be a better exception.');
        }
        $outer = function() use($f, $outer) {
            return $f(call_user_func_array($outer, func_get_args()));
        };
    }
    return $outer;
}

$password = 'PASSWORD';

$rot13 = compose('str_rot13');
// Hide our password from kid sister:
print $rot13($password) . "\n";

$doubleRot13 = compose($rot13, 'str_rot13');
// Whoops, overshot that one:
print $doubleRot13($password) . "\n";

$uberHasher = compose('sha1', 'md5', 'crc32');
// A REALLY SUPER ULTIMATE SECURE HASH:
print $uberHasher($password) . "\n";