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MonoidLaws.php
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MonoidLaws.php
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<?php
declare(strict_types=1);
namespace FunctionalPHP\FantasyLand\Helpful;
use FunctionalPHP\FantasyLand\Monoid;
use function FunctionalPHP\FantasyLand\concat;
use function FunctionalPHP\FantasyLand\emptyy;
class MonoidLaws
{
/**
* 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
) {
$assertEqual(
concat($x, emptyy($x)),
$x,
'Right identity'
);
$assertEqual(
concat(emptyy($x), $x),
$x,
'Left identity'
);
$assertEqual(
concat($x, concat($y, $z)),
concat(concat($x, $y), $z),
'Associativity'
);
}
}