Monad in PHP?!

monad.php

<?php
/**
 * Monad boxing integer side effects
 *
 * @package default
 * @subpackage default
 * @author Federico Marani
 **/
class IntegerBox
{
    /**
     * undocumented function
     *
     * @return void
     **/
    public function __construct($value)
    {
        $this->value = $value;
        $this->isNaN = false;
        $this->infinite = false;
    }
    /**
     * undocumented function
     *
     * @return void
     **/
    public static function identity($unboxedInt)
    {
        return new IntegerBox($unboxedInt);
    }

    /**
     * undocumented function
     *
     * @return void
     **/
    public static function bind($boxedInt, $function)
    {
        $newBox = @$function($boxedInt);
        if ($newBox->value == null)
            $newBox->infinite = true;
        return $newBox;
    }

    /**
     * undocumented function
     *
     * @return void
     **/
    public function __toString()
    {
        if ($this->isNaN)
            return "NaN";
        if ($this->infinite)
            return "Infinite";
        return strval($this->value);
    }
} // END class IntegerBox

$plusOne = function($x) { return IntegerBox::identity($x->value + 1); };

$one = IntegerBox::identity(1);

$two = IntegerBox::bind($one, $plusOne);

print "$two\n";

$divideByZero = function($x) { return IntegerBox::identity(bcdiv($x->value, 0)); };

$newVal = IntegerBox::bind($one, $divideByZero);

print "$newVal\n";