On Tue, Sep 15, 2020 at 7:31 PM Benjamin Peterson <benja...@python.org> wrote:
> On Tue, Sep 15, 2020, at 20:10, Greg Ewing wrote: > > Maybe the PEP should propose an AST of its own, which would initially > > be a third thing separate from either of the existing ones, with > > the possibility of adopting it as the ast module representation > > some time in the future. > > The rust approach to this problem to pass only a token stream to the > macro. Then, the macro writer brings their own parser. > And (I looked this up [1]) it returns another token stream which is then re-parsed by the standard parser. I'm not quite sure who is responsible for determining where the macro ends -- the standard parser or the macro parser. A nice side effect of this would be that (hopefully) the macro syntax doesn't need to have the ugly special cases needed to allow `import! foo as bar` and `from! mod import foo as bar` (though these still need to be predefined macros). I'm not entirely sure how this would preserve the hygiene of the macros though, since the macro's parser could just do a token-by-token substitution without checking the context, effectively what a macro in C does. Forcing an AST on the macros restricts macros somewhat (e.g. it requires the input arguments to look like well-formed expressions) but that's probably a good thing. (Hm, or not. How would you implement something like PEP 505 using macros? It introduces new tokens like `?.` and `??`. [1] https://doc.rust-lang.org/book/ch19-06-macros.html -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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