Innmind / Immutable

    {

        $map = $this->clear();

        foreach ($this->keys as $index => $key) {

            $return = $function(

                $key,

                $this->values->get($index)

            );

            if ($return instanceof Pair) {

                $key = $return->key();

                $value = $return->value();

            } else {

                $value = $return;

            }

            $map = $map->put($key, $value);

        }

        return $map;

    }

        $truthy = $this->clear();

        $falsy = $this->clear();

        foreach ($this->keys as $index => $key) {

            $return = $predicate(

                $key,

                $value = $this->values->get($index)

            );

            if ($return === true) {

                $truthy = $truthy->put($key, $value);

            } else {

                $falsy = $falsy->put($key, $value);

            }

        }

        return (new self('bool', MapInterface::class))

            ->put(true, $truthy)