example1.php

<?php

$maybeDelayedMessage = $this->delayedMessages->getNext();

if (!$maybeDelayedMessage instanceof Some) {
    $this->connection->rollBack();
    sleep(10);

    return;
}

/** @var DelayedMessage $delayedMessage */
$delayedMessage = $maybeDelayedMessage->extract();

example2.php

<?php

$maybeOverlappingAppointment = $this->appointments->getOverlapping($date);
$maybeOverlappingAppointment->ifSome(function (Appointment $overlappingAppointment) {
    throw new CannotCreateAppointment(
        \sprintf(
            'Schedule of appointment with ID %s overlaps with appointment with ID %s.',
            $appointmentId1,
            $appointmentId2
        )
    );
});

functions.php

<?php

function none(): Maybe
{
    return new class() implements None {
        public function ifSome(callable $f): Maybe
        {
            return none();
        }
    };
}

function some($value): Maybe
{
    return new class($value) implements Some {
        private $value;

        public function __construct($value)
        {
            $this->value = $value;
        }

        public function extract()
        {
            return $this->value;
        }

        public function ifSome(callable $f): Maybe
        {
            return $f($this->extract()) ?? $this;
        }
    };
}

Maybe.php

<?php

interface Maybe
{
    public function ifSome(callable $f): self;
}

None.php

<?php

interface None extends Maybe
{
}

Some.php

<?php

interface Some extends Maybe
{
    public function extract();
}