SE-0351: Regex Builder DSL

[xAlien95 (Stefano De Carolis)]

@Michael_Ilseman

My dream is named captures via let bindings inside the result builder, allowing you to interact with them later in the builder as a kind of Swift take on backreferences. Something like monadic bind would allow you to accumulate and forward values (though I don't know enough about result builder design rationale to know whether this is sacrilege).

Since this is also my dream, I am afraid that allowing statements within the builder will preclude this eventuality. It's also unfortunate to have regular expression literals having labeled captures (which, in Swift, I guess will happen almost 100% of the times) to break code when converted into a combination of Regex DSLs and References. Ideally, you shouldn't do anything after converting a regex literal into its DSL equivalent.

Also, is the current design capable of placing labeled regexes in Regex DSLs or are labeled tuples not handled by the 10-nple overloads?

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Should the transform closure on Try/Captures become a .transform method on instances of RegexComponent? It could be useful to be able to try a transformation without actually capturing the value.

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Regarding the Structured rather than flat captures final section in the considered alternatives: I'm not sure it's a future-proof decision to split Regex and an hypothetical Pattern based on their capture structure and default semantics. If a more powerful, "Swifty" and structured Pattern is available, would users still use this hybrid Regex DSL?