public static function fmap(callable $f, $a)
{
assert($a instanceof Instance, 'Second argument must be Either');
if ($a instanceof Instance\Left) {
return $a;
}
return Right($f($a->value));
}
public static function ap($mf, $a)
{
return f(function (Instance $mf, Instance $a) {
if ($mf instanceof Instance\Left || $a instanceof Instance\Left) {
return $fm;
}
$f = $mf->value;
return Right($f($a->value));
}, $mf, $a);
}
/**
* Converts Some to a Right, else it becomes a Left containing the return of $left
* @param callable $left a function holder for some alternative value
* @return Left|Right
*/
public function toRight(callable $left)
{
return $this->isEmpty() ? Left(call_user_func($left)) : Right($this->get());
}
function testRight()
{
$this->assertEquals('df', Right("asdf", 2), 'Test1');
$this->assertEquals('', Right("asdf", 0), 'Test2');
}