either.md

Either

Almost that same as Maybe but it holds two values, the right one aka success, and the left aka error.

Lets took the same example from Maybe but change it a bit.

class ArticlesRepository
{
    public function get(int $id): Either
    {
        try {
            return Either::right($this->entityManager->get($id));
        } catch (DatabaseException $exception) {
            return Either::left($exception);
        }
    }
}

$articleTitle = $repository->get(120)->map(prop('title'))->map(take(22))->map('strtoupper');

We can safely apply the same functions (like take and strtoupper) to our value.

Then somewhere in your code:

$articleTitle->match(
    partial([$view, 'addVar'], 'articleTitle'),
    [$errorHandler, 'handle']
);

// Equals to

$possibleArticleTitle = $articleTitle->extract();
if ($possibleArticleTitle) {
    $view->addVar('articleTitle', $possibleArticleTitle);
} else {
    $errorHandler->handle($possibleArticleTitle);
}