In a recent post to his site Marco Perone looks at the idea of "maybe" in PHP, having functionality that acts a default value if no value is present. This idea is implemented in other languages like Haskell and Elm.

Doing functional programming in a language as PHP, which is almost completely used as an imperative or object oriented way, is not always easy. Good progresses have been made thanks to the introduction of callable type hints in PHP 5.4 and the diffusion of functional interfaces like the ones present in PSR-7.

Still, all “good” PHP code is still written using objects and classes and the object oriented perspective on the world strongly influences even the most functional oriented libraries.

In this post I would like to propose as an example how we could implement the Maybe type in PHP. We will see how some open source libraries do this, we will see an alternative solution and we will raise concerns about some modelling issues.

He starts off by describing what the "maybe" functionality is and gives some examples of it in use in other languages. He points out that while there's several PHP libraries that implement this kind of default handling, it's not in the PHP core language. He works through some of these libraries and shows them in use: monad-php, Phunkie, php-maybe-monad and php-fp-maybe. He wraps up the post showing his own suggested implementation and how it could help resolve some of the issues he found with the other libraries as he worked through them.