README

A Maybe monad implementation for PHP

This project was wholly inspired by a blog post by @linepogl.

Motivation

Dealing with null values (and, in PHP, falsy values) is tedious and prone to developer error (viz the null pointer exception, trying to dereference a null).

In my exposure to Haskell, I learned about the awesomeness of pattern matching, whereby you can get the compiler to force yourself to handle all possibilities. This combines with a tool called Maybe to require specific handling for "null" and "non-null" possibilities.

PHP does not offer pattern matching, but we can still use classes to wrap raw values, and require us to handle null conditions, without repeated explicit null checking and conditionals.

Examples

Simple

Before:

$blogpost = $repository->get($blogpostId);
echo $blogpost->teaser();  // oh noe! what if $blogpost is null?! :boom:

After:

$blogpost = new \Yitznewton\Maybe\Maybe($repository->get($blogpostId));
echo $blogpost->select(function ($bp) { $bp->teaser(); })->valueOr('No blogpost found');

With callback

$blogpost = new \Yitznewton\Maybe\Maybe($repository->get($blogpostId));
$callback = function () {
    return someExpensiveOperation();
};
echo $blogpost->select(function ($bp) { $bp->teaser(); })->valueOrCallback($callback);

Loose-falsy

// $process->execute() normally returns a result object, but sometimes returns false
$result = new LooseMaybe($process->execute());

echo $result->select(function ($resultObject) { $resultObject->getStatus(); })->valueOr('failed');
// echoes 'failed' when the result was false

Performance

In a simple test using PHP 5.5, performance was approximately 20% that of a straight is_null() check in an if/else conditional. In other words it takes 5 times as long to run.

You can reproduce the test locally by running the profiling testsuite in PHPUnit. You will first need to install XHProf, and override the XHProf lib directory using a local phpunit.xml config.

$ ./vendor/bin/phpunit --testsuite=profiling

Dictionary wrapper

maybe-php includes an array wrapper called Dictionary, whereby trying to access properties on the wrapper will return a Maybe object. You can specify whether to return a plain Maybe (default) or a LooseMaybe.

$dictionary = new \Yitznewton\Maybe\Dictionary([
    'foo' => 'bar',
]);

$dictionary->foo->valueOr('quux');        // 'bar'
$dictionary->noSuchKey->valueOr('quux');  // 'quux'

// with LooseMaybe

$dictionary = new \Yitznewton\Maybe\Dictionary([
    'foo' => false,
], \Yitznewton\Maybe\LooseMaybe::class);

$dictionary->foo->valueOr('quux'); // 'quux', because loose falsy