Functional Programming in PHP

gistfile1.php

<?php
class MyList implements ArrayAccess
{
	private $_values;

	public function __construct($array = array())
	{
		$this->_values = $array;
	}

	public function cons($a)
	{
		if (!is_int($a)) throw new InvalidArgumentException();
		array_unshift($this->_values, $a);
		return $this;
	}

	public function head()
	{
		return $this->_values[0];
	}

	public function tail()
	{
		return new MyList(array_slice($this->_values, 1));
	}

	public function sum0()
	{
		if (empty($this->_values)) return 0;
		return $this->head() + $this->tail()->sum0();
	}

	public function reduce($f, $a)
	{
		if (empty($this->_values)) return $a;
		return $f($this->head(), $this->tail()->reduce($f, $a));
	}

	public function sum()
	{
		return $this->reduce($this->add(), 0);
	}

	public function add()
	{
		return function ($a, $b) { return $a + $b; };
	}

	public function product()
	{
		return $this->reduce($this->multiply(), 1);
	}

	public function multiply()
	{
		return function ($a, $b) { return $a * $b; };
	}

	public function any_true()
	{
		return $this->reduce($this->_or(), false);
	}

	public function all_true()
	{
		return $this->reduce($this->_and(), true);
	}

	public function _or()
	{
		return function ($a, $b) { return ($a === true || $b === true); };
	}

	public function _and()
	{
		return function ($a, $b) { return $a === true && $b === true; };
	}

	public function _cons()
	{
		return function ($a, $b) { return $b->cons($a); };
	}

	public function dup()
	{
		return $this->reduce($this->_cons(), new MyList());
	}

	public function append($ls)
	{
		return $this->reduce($this->_cons(), $ls);
	}

	public function double_all()
	{
		return $this->reduce($this->double_and_cons(), new MyList());
	}

	public function double_and_cons()
	{
		return function ($a, $ls) { return $ls->cons($a * 2); };
	}

	public function offsetExists($offset)
	{
		return isset($this->_values[$offset]);
	}

	public function offsetGet($offset)
	{
		if (isset($this->_values[$offset])) {
			return $this->_values[$offset];
		}
		return null;
	}

	public function offsetSet($offset, $value)
	{
		if (!is_int($offset)) throw new InvalidArgumentException("You can't use as a Hash.");
		$this->_values[$offset] = $value;
	}

	public function offsetUnset($offset)
	{
		unset($this->_values[$offset]);
	}
}


$ma = new MyList(array(1, 2, 3, 4, 5));
var_dump($ma->sum0());// 15

$ma = new MyList();
var_dump($ma->cons(1)->cons(2)->cons(3)->sum0());// 6

$ma = new MyList(array(1, 2, 3, 4, 5));
$r = $ma->reduce(function($a, $b) { return $a + $b; }, 0);
var_dump($r);// 15

$ma = new MyList(array(1, 2, 3, 4, 5));
var_dump($ma->sum());// 15

$ma = new MyList(array(1, 2, 3, 4, 5));
var_dump($ma->product());// 120

$ma = new MyList(array(false, true, false));
var_dump($ma->any_true());// true
var_dump($ma->all_true());// false

$ma = new MyList(array(true, true, true));
var_dump($ma->any_true());// true
var_dump($ma->all_true());// true

$ma = new MyList(array(1, 2, 3));
var_dump($ma->dup());
var_dump($ma->append(new MyList(array(4, 5, 6))));

$ma = new MyList(array(1, 2, 3, 4, 5));
var_dump($ma->double_all());