nishimura/laiz-monad

<?php

namespace Laiz\Func;

interface Functor
{
    public static function fmap(callable $f, $a);
}

namespace Laiz\Func\Functor;

use Laiz\Func\Loader;
use Laiz\Func\Any;
use function Laiz\Func\_callInstanceMethod;
use function Laiz\Func\f;
use function Laiz\Func\cnst;

// (<$>) :: Functor f => (a -> b) -> f a -> f b
function fmap(...$args)
{
    $f = function(callable $f, $a){
        return Loader::callInstanceMethod($a, 'fmap', $f, $a);
    };
    if (count($args) === 2)
        return $f(...$args);
    else
        return f($f, ...$args);
}

// (<$) :: Functor f => a -> f b -> f a
function fconst(...$args)
{
    $ret = fmap()->compose(cnst());
    if ($args) $ret = $ret(...$args);
    return $ret;
}