Byte-sized functional programming: Pure functions encourage small code

One of the many pieces of advice for a long-term sustainable code base is to keep code small. The larger a code base is, the more effort it takes to understand all the moving parts. Your brain can only keep so much mental model of your code in it at once, and if the code you're looking at is too large then what you can fit in your own "active memory" at once then you will have an increasingly hard time understanding it.

Most useful applications tend to grow larger than what the typical human can fit in their active memory, however, so you need a way to break up your code so you can load a relevant piece into your brain at once to understand and debug it. Usually that takes the form of encapsulation, coupling, cohesion, and other common object-oriented vernacular.

But what about just a pure function?

A pure function is a function that:

  • has no inputs other than those explicitly specified;
  • has no effect on any value other than the value it returns.

That has a number of advantages, such as being idempotent (calling it a second time with the same values is guaranteed to return the same result) and referential transparency (a function and its parameters is synonymous with its result, which can let you optimize the function away entirely in some cases). But perhaps the biggest advantage of pure functions doesn't have a fancy name: It's really easy to fit in your brain.

If you're trying to understand a given piece of code, a pure function will always be the easiest to understand because there is no need for context. There are some explicit inputs, which you can see; There is an explicit output, which you can see; And there's nothing else to care about. Reading the function (and the data definition of its parameters) is all you need to think about, because there's nothing else to think about. Every function becomes a natural "small enough to fit in your brain" unit.

A pure function will often call other pure functions, but that only creates slightly more overhead. Once you know a function is pure, it's easy to mentally "unload" as a black box that you can deal with separately. Go read that code first, then put it out of your brain and focus on the next function.

Moreover, functional programming-style code tends to favor function composition over direct function calls. That is, rather than function A calling function B which calls function C, you call function A and pass its return value to function B, then pass B's return value to C. That whole process can be wrapped up into another function if necessary. That makes it even easier to focus on only one function at a time, which is virtually guaranteed to fit in your brain at once.


Want to know more about functional programming and PHP? Read the whole book on the topic: Thinking Functionally in PHP.

Thinking Functionally in PHP
Larry 6 July 2020 - 5:13pm
A Major Event in PHP ebook now available

In early 2019, the PHP Framework Interoperability Group (PHP-FIG) released PSR-14, the Event Dispatcher specification. At the time I posted a long series of blog posts detailing PSR-14 in all its glory.

After discussing with a few other FIG folks, I've decided to release that blog series as a small ebook. Mainly that is to provide an easy single-point-of-reference for those who want to really understand PSR-14. Also, it serves as a simple fundraiser.

The book itself is available completely free, as the original blog posts were. However, you can also purchase a copy if you want to help support my work on the Framework Interoperability Group and Open Sourcing Mental Illness. OSMI is a non-profit organization that works to raise awareness of and research information about mental health challenges in the tech community. 50% of all royalties for this book are automatically donated to OSMI to support their vital work.

If you just want to grab a copy for free, go for it. If you are able to, though, I would encourage you to pay what you're comfortable with to support both my Open Source efforts and OSMI.

(This announcement is a bit late due to a publishing goof on my blog. If you're seeing this for the second time, my apologies.)

Larry 6 July 2020 - 5:12pm

Type Matching in PHP

Submitted by Larry on 2 February 2020 - 1:46pm

One of the nice features of Rust is the match keyword. match is similar to `switch`, but with two key differences:

  1. It requires an exhaustive match, that is, every possible value must be accounted for or a default must be provided.
  2. match is an expression, meaning you can assign the return value of one of its branches to a variable.

That makes match extremely useful for ensuring you handle all possibilities of an enumerated type, say, if using an Optional or Either for error handling. Which... is something I've been experimenting with in PHP.

It's hard to make a PHP equivalent of match that forces an exhaustive match, as PHP lacks enumerated types. However, emulating an expression match turns out to be pretty easy in PHP 7.4, and kind of pretty, too.

Skipping PHP.CE this year

Submitted by Larry on 19 July 2019 - 7:01pm

Being a conference organizer is hard. Like, seriously. Aside from the obvious logistics, and the not-at-all-obvious logistics, you're in a position to create a social gathering, not just a technical one. That comes with a lot of baggage and challenges, many of them often competing and incompatible, that need to be balanced. One in particular is ensuring that the speakers are an eclectic lot that are representative both of the community as it is and as you want it to be. That can take a lot of work.

Earlier this year the organizers of the PHP Central Europe conference (PHP.CE) approached me and asked me to submit sessions for the PHP.CE conference in Dresden this October. I rather enjoy speaking at conferences so I of course did so, and this past week they announced their speaker selections, including me with 2 sessions.

Unfortunately, some fellow speakers pointed out that their speaker selections for this year included zero women. There were numerous speakers with 2 sessions (myself included) or a workshop and a session, but no women at all.

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On "10x developers"

Submitted by Larry on 14 July 2019 - 11:58am

Yesterday, a VC posted a Twitter thread about "10x engineers and how to spot them.'' It is a frankly terrible thread, and predictably, it became the latest Internet Pile On(tm), which we all know is Twitter's favorite pastime. I added my own thoughts in another thread, which I want to replicate here for posterity and then expand on a bit more now that I have a real keyboard and not just my phone.

First, here's my original thread, lightly edited for clarity, paragraphs, and links:

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I was wrong about PSR-11

Submitted by Larry on 15 June 2019 - 2:43pm

Back in January 2017, the PHP Framework Interoperability Group (FIG) reviewed and passed PSR-11, the "Container Interface" specification. It was a very simplistic 2-method interface for Dependency Injection Containers, which had been worked on for some time by a small group. (This was before FIG had formal Working Groups, but "container-interop" was one of the effectively proto-Working Groups that were floating about.)

PSR-11 passed overwhelmingly, 23 to 1 out of the FIG member projects at the time. The lone holdout was Drupal, for which at the time I was the voting representative.

Two and a half years later, I will say I was wrong, and PSR-11 has been a net-win for PHP.

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PSR-14: Example - layered caching

Submitted by Larry on 14 May 2019 - 2:18pm

So far we've looked at a number of complete, practical examples of using PSR-14 Events in various ways, both conventional and unconventional. In our final (probably) installment, I want to offer a highly unconventional but still practical use of PSR-14 that really shows off just how flexible Events can be: Layered caching.

"But wait, isn't caching the realm of PSR-6 and PSR-16?" Yes. Yes it is. But neither of those offer a built-in way to compose multiple cache backends together. It's certainly possible, but doing so is left as an exercise for the implementer. Let's use PSR-14 to get some exercise.

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PSR-14: Example - PSR-14 in a non-blocking application server

Submitted by Larry on 29 April 2019 - 3:51pm

We continue our exploration of PSR-14's potential with a guest post. Cees-Jan Kiewiet was the Sponsor of PSR-14 (meaning the member of the Core Committee who bridged from the Working Group to the Core Committee), and is on the core team for ReactPHP. One wouldn't think there's any use cases for PSR-14 in an async environment like React, but one would be wrong.

Here's Cees-Jan with an explanation:

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PSR-14: Example - Delayed Events, Queues, and Asynchronicity

Submitted by Larry on 26 April 2019 - 5:34pm

One of the long-running debates while designing PSR-14 was how to handle events that were inherently mono-directional. Often, a library will trigger an Event that is, from its point of view, entirely informational. The Event object it fires has no mutator methods so Listeners have no way to interact with each other, which means that the order Listeners run in is irrelevant. It also means Listeners can pass no data back to the emitting library, which means the result of the Event can have no impact on the Emitter's further logic.

This special case opens up more options for how to execute the Listeners. Because there is guaranteed no communication from Listener to Listener or from Listener to Emitter, it's safe to run the Listeners concurrently. In fact, it's safe to run the Listeners concurrently with the Emitter. The Emitter doesn't even need to wait for the Listeners to fire before continuing.

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