PHP Internals News: Episode 103: Disjunctive Normal Form (DNF) Types

PHP Internals News: Episode 103: Disjunctive Normal Form (DNF) Types

Friday, June 24th 2022, 09:07 BST London, UK

In this episode of "PHP Internals News" I talk with George Peter Banyard (Website, Twitter, GitHub, GitLab) about the "Disjunctive Normal Form Types" RFC that he has proposed with Larry Garfield.

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Transcript

Derick Rethans 0:15

Hi, I'm Derick. Welcome to PHP internals news, a podcast dedicated to explaining the latest developments in the PHP language. This is episode 103. Today I'm talking with George Peter Banyard again, this time about a disjunctive normal form types RFC, or DNF, for short, which he's proposing together with Larry Garfield. George Peter, would you please introduce yourself?

George Peter Banyard 0:39

Hello, my name is George Peter Banyard, I work on PHP paid part time, by the PHP foundation.

Derick Rethans 0:44

Just like last time, we are still got colleagues.

George Peter Banyard 0:46

Yes, we are indeed still call it.

Derick Rethans 0:48

What is this RFC about? What is it trying to solve?

George Peter Banyard 0:52

The problems of this RFC is to be able to mix intersection and union types together. Last year, when intersection types were added to PHP, they were explicitly disallowed to be used with Union types. Because: a) mental framework, b) implementation complexity, because intersection types were already complicated on their own, to try to get them to work with Union types was kind of a big step. So it was done in chunks. And this is the second part of the chunk, being able to use it with Union types in a specific way.

Derick Rethans 1:25

What is the specific way?

George Peter Banyard 1:27

The specific way is where the disjoint normal form thing comes into play. So the joint normal form just means it's a normalized form of the type, where it's unions of intersections. The reason for that it helps the engine be able to like handle all of the various parts it needs to do, because at one point, it would need to normalize the type anyway. And we currently is just forced on to the developer because it makes the implementation easier. And probably also the source code, it's easier to read.

Derick Rethans 1:54

When you say, forcing it up on a developer to check out you basically mean that PHP won't try to normalize any types, but instead throws a compilation error?

George Peter Banyard 2:05

Exactly. It's, it's the job of the developer to do the normalization step. The normalization step is pretty easy, because I don't expect people to do too many stuff as intersection types. But as can always b