Ok, here is a discussoin using code in syntax-parse. Let's start with the defintion of a syntax-class, str in the macro package syntax-parse: (define-syntax-class str #:attributes () #:opaque #:commit #:description "string" (pattern (~and x (~fail #:unless (string? (syntax-e #'x))))))
So the and patterns first match x and then on the same element match a ~fail that fails if the supplied code (string? (syntax-e #'x)) is false. The headake for me is that #'(string? (syntax-e #'x)) is stored in a struct and hence does not get wrapped correctly e.g. after the packaging of this code in a struct, say S we will then issue something like the following code in the expansion of the first match #'(with-syntax ((x stx)) (parse stx S)) and when parse is ready to unpack S we could have S = #(syntax-object #<struct-s> wrap-part hygiene) Now I basically solve this problem by constructing a = (vector 'syntax-object (vector-ref (struct-s-code (syntax->datum S)) 1) (un-mark wrap-part) hygiene) crossing the fingers that the "code" will be nonatomic and then the expander will use it like, (with-syntax ((code a)) #'( .... code)) This is the story. I do not want to rest here because this solution is not resistant to bitrot and depends on internals that I do not want to touch. The solution would be to have an interface in guile that allows to write, (with-syntax ((code (syntax-embedd (struct-s-code (syntax->datum S)) S))) (.... code ...)) e.g. (syntax-embedd exp env-stx) = embedds exp in the syntax env-stx I'm much more fine with dropping env-stx and replace that with the equivalent syntax environment at the macro call I Hope that things are less foggy now! Regards Stefan On Mon, Jan 23, 2012 at 11:53 AM, Andy Wingo <wi...@pobox.com> wrote: > Hi Stefan, > > On Thu 19 Jan 2012 10:50, Stefan Israelsson Tampe <stefan.ita...@gmail.com> > writes: > > > Working on porting syntax-parse is a learning experience and I know > > understand how it uses syntax-local-value as a way to lookup a syntax > > object by joining the wraps together with the total wrap at the macro > > call. > > syntax-local-binding just uses the wrap from the id that you give it, > without joining it to the macro expansion environment's wrap. > > > I would like to have a syntax-join function that takes two syntax > > objects and join them correctly and robustly in the pressense of > > eventual marks or not. > > Why would you want to do something like this? > > You might try writing the documentation of the function first; it would > clarify the conversation. > > Regards, > > Andy > -- > http://wingolog.org/ >
