Plus

The Plus typeclass provides monoid-like operations on type constructors instead of values.

Parent

The Plus typeclass extends the Alt typeclass.

The Plus typeclass provides a single method, which returns the identity element of the alt operation defined by the Alt instance.

interface Plus extends Alt
{
    /**
     * @return F<A>
     */
    public function empty();
}

Its simplified type is

empty :: () -> F<A>

The Plus typeclass requires several laws to hold, in addition to the ones required by the Alt typeclass.

$alternative->alt($alternative->empty(), $x) == $x

$alternative->alt($x, $alternative->empty()) == $x

$alternative->map($f, $alternative->empty()) == $alternative->empty()