/**
* @inheritdoc
*
* fs <*> xs = [f x | f <- fs, x <- xs]
*/
public function ap(FantasyLand\Apply $applicative)
{
return $this->reduce(function ($accumulator, $value) use($applicative) {
/** @var $applicative self */
return f\concatM($accumulator, $applicative->map($value));
}, self::mempty());
}
public function test_foldr()
{
$list = Listt::of([1, 2, 3, 4]);
$result = f\foldr(function ($accumulator, $value) {
return f\concatM($accumulator, Listt::of([$value + 1]));
}, Listt::of([]), $list);
$this->assertEquals($result, Listt::of([5, 4, 3, 2]));
}
/**
* Generic test to verify if a type obey the monodic laws.
*
* @param callable $assertEqual Asserting function (Monoid $m1, Monoid $m2, $message)
* @param Monoid $x
* @param Monoid $y
* @param Monoid $z
*/
public static function test(callable $assertEqual, Monoid $x, Monoid $y, Monoid $z)
{
$assertEqual(f\concatM($x, f\emptyM($x)), $x, 'Right identity');
$assertEqual(f\concatM(f\emptyM($x), $x), $x, 'Left identity');
$assertEqual(f\concatM($x, f\concatM($y, $z)), f\concatM(f\concatM($x, $y), $z), 'Associativity');
}
