SE-0354: Regex Literals

[Michael_Ilseman]

@Karl

I remember some of the previous proposals mentioned having user types which could be expressed as Regex literals. Is that part of another proposal or has it been dropped (at least for now)?

That is future work. The ExpressibleBy* approach is geared around the needs of data literals, which it barely serves. Regex literals are more akin to algorithm literals. Thus, I think it is better to improve the library-compiler interface here. From an early thread:

@Michael_Ilseman

Library-extensibility

We're jettisoning the fine-grained protocol approach that's pitched. It's proving to be unnecessary for the stdlib thanks to this library-oriented architecture for the parser. Most conceivable conformers (e.g. a libPCRE2 wrapper) would just want to pass off the raw, unprocessed content of the string to someone else anyways.

I'm still very interested and excited by library-extensibility here. I think making the parser's AST available to libraries is a much better extensibility story than serializing the information through low-level builder.buildConcatenate() calls. This can be evolved over time, and though we're designing for this to happen in the future, it will likely land later than more fundamental functionality.

Even better than raw mode is the ability for the regex parser to pretty-print its AST using a requested syntax variant.

Either way this is incremental and future work. Nothing in the proposal precludes this.

@Karl

I may want/need a deeper understanding of the AST or the ability to construct my own type from a user's literal (or restrict some regex features).

This is a fascinating use case and I'm really interested in exploring it! (outside the scope of this specific proposal, of course).