Whitebox def macros

[LPTK]

@retronym

I’d like a way for whitebox macros authors to be able (although not neccesarily obliged) to separate the part of the macro that computes the return type from the part that computes the expanded term. Let’s call the first part “signature macros”.

Sounds like the most natural way to do it would be to just have type macros. Then whitebox macros are just blackbox macros with a return type that is a macro invocation.

def myWhitebox[A](a: A, str: String): MyReturn[A, str.type] = macro ...
type MyReturn[A, S <: String with Singleton] = macro ...

It’s a nice separation of concerns. But I’m afraid there are a lot of whitebox macros in the wild where both code generation and type refinement are very much intertwined, because they’re semantically inseparable. In the case of Squid, what I’d do is to parametrize the current macro to either just compute a type or do the full code generation; but that would mean a lot of computation would be duplicated (I would have to parse, transform, typecheck and analyse the quasiquote string in both type signature and code-gen macro invocations), and batch compile times would be strictly worse.