Fun with ‘anonymous’ functions in PHP

<?php

    class LambdaException extends Exception {}
    class Lambda
    {
        private static $cache;

        public static function Create($functionString)
        {
            if(!isset(self::$cache[$functionString]))
            {
                list($args, $body) = self::BreakupFunctionString($functionString);
                self::$cache[$functionString] = new self($args, $body);
            }

            return self::$cache[$functionString];
        }

        private static function BreakupFunctionString($functionString)
        {
            $errorMessage = "Unable to understand the function: '$functionString'." .
                            "Format should follow function (\$arg1, \$arg2) { return rand(\$arg1, \$arg2); }";

            $regex = "^function\s*\(([^\)]*)\)\s*\{(.*?)\}$";
            if(preg_match("#$regex#si", trim($functionString), $matches) !== 1)
            {
                throw new LambdaException($errorMessage);
            }

            list(, $args, $body) = $matches;

            $args = explode(',', $args);
            $args = array_map('trim', $args);
            $args = array_diff($args, array(''));

            return array($args, $body);
        }

        //--------------------------------------------------------------------


        private $args;
        private $body;
        private $function;

        private function __construct($args, $body)
        {
            assert('is_array($args)');
            assert('is_string($body)');

            $this->args = $args;
            $this->body = $body;
            $this->function = create_function(implode(',', $this->args), $this->body);
        }

        public function map($array)
        {
            //  We could actually test if the number of args is two
            //  and do a array_map with keys as well
            assert('count($this->args) == 1');
            return array_map($this->function, $array);
        }

        public function filter($array)
        {
            assert('count($this->args) == 1');
            return array_filter($array, $this->function);
        }

        public function sort($array)
        {
            assert('count($this->args) == 2');
            usort($array, $this->function);
            return $array;
        }

        public function call()
        {
            $args = func_get_args();

            return call_user_func_array($this->function, $args);
        }

        public function getFunction()
        {
            return $this->function;
        }

        public function __toString()
        {
            return $this->function;
        }
    }

    $extractRowId = Lambda::Create('function ($row) { return $row["id"]; }');
    print_r($extractRowId->map(array(array('id' => 'a'), array('id' => 'b'))));

    $randomise = Lambda::Create('function ($v, $v) { return rand(0,1) == 0 ? -1 : 1; }');
    print_r($randomise->sort(array(1, 2, 3, 4, 5, 6, 7, 8, 9)));

    $greaterThanFive = Lambda::Create('function ($var) { return $var > 5; }');
    print_r(array_filter(array(1,2,3,4,5,6,7,8,9), $greaterThanFive->getFunction()));
    print_r(array_filter(array(1,2,3,4,5,6,7,8,9), (string)$greaterThanFive));

    $printString = Lambda::Create('function($str) { echo $str . "\n"; }');
    $printString->call("Hello World");


    function formatString($s)
    {
        $args = func_get_args();

        for($i = 1; $i < count($args); $i++)
        {
            $s = $args[$i]->call($s);
        }

        return $s;
    }


    $italic = Lambda::Create('function($s) { return "<i>" . $s . "</i>"; }');
    $bold   = Lambda::Create('function($s) { return "<bold>" . $s . "</bold>"; }');

    $tag        = Lambda::Create('function($t) { return Lambda::Create("function(\$s) { return \"<$t>\" . \$s . \"</$t>\"; }"); }');
    $heading    = $tag->call('h1');
    $para       = $tag->call('p');

    echo formatString('Weird Formatting', $italic, $bold, $heading) . "\n";


    $content    = Lambda::Create('function($s) { return "Hello Lambda!" . $s; }');
    $newLine    = Lambda::Create('function($s) { return $s . "<br/>"; }');

    echo formatString('', $content, $bold, $italic, $newLine, $para) . "\n";

?>

Array
(
    [0] => a
    [1] => b
)
Array
(
    [0] => 7
    [1] => 1
    [2] => 5
    [3] => 4
    [4] => 3
    [5] => 6
    [6] => 2
    [7] => 8
    [8] => 9
)
Array
(
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
)
Array
(
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
)
Hello World
<h1><bold><i>Weird Formatting</i></bold></h1>
<p><i><bold>Hello Lambda!</bold></i><br/></p>