The regular formalism is, fundamentally, about composition, and the current syntax doesn't do it justice.

That syntax was devised as a math notation, where sub-patterns were abstracted as one letter variables. You didn't have to deal with complex patterns at all, and it was very readable for that use case.

It was then re-purposed as a write-only language for searching at the CLI (in `ed` and its descendants, then grep).

They gradually graduated into what they are today in general programming languages because they were familiar and worse is better... However, composition got lost in the process.

Swift takes a radically different approach, and gives RegExps a parser combinator syntax. So every sub-expression can be assigned to a variable and reused/tested independently.

Here's an example (sorry I don't have it at hand in text form): https://pbs.twimg.com/media/FipgjUdUcAAl1xS?format=jpg&name=...

I wrote a lib that does the same in JS (the lib predates the Swift syntax by years). Here's the same example ported to JS: https://flems.io/#0=N4IgtglgJlA2CmIBcBWAzAOgAwCYA0IAzgMYBOA9...

Here's the lib: https://github.com/compose-regexp/compose-regexp.js