Thanks Neil for the ideas! I didn't think of looking how 'all-from-out' works so I will start from there!
2011/11/9 Neil Toronto <[email protected]> > On 11/09/2011 07:29 AM, Ismael Figueroa Palet wrote: > >> Hi all, please help me with the following: >> >> I need to require a module, ideally with the same syntax as require, >> then access to all the imported symbols and re-export them with the same >> name but with a new definition, that is a wrapper for the original one. >> >> I think this should be done with a macro, but I don't know how to access >> the imported symbols acquired with require. >> >> any pointers to documentation or ideas on how to implement this? >> > > You'll want to implement something similar to `all-from-out'. I don't know > exactly how it works; specifically, how it gets a list of imported > identifiers. It's a "provide transformer" - you can search for that term in > the docs. Also, don't be afraid to look at the code for `all-from-out'. > It's defined in "collects/racket/private/**reqprov.rkt". > > Random tips: > > You'll need to make a provide transformer (using > `make-provide-transformer) or a provide "pre-transformer" (using > `make-provide-pre-transformer'**). Pre-transformers are expanded first, > and return new provide syntax. Transformers are then expanded, and they > return "exports", which are structs that contain information about provided > symbols. In either case, you can get away with just manipulating syntax. > > Unlike regular macros, provide macros don't automatically expand until > they expand into a basic form. If, say, in a pre-provide macro, you return > new provide syntax that's *not* a basic provide form, you'll need to use > `pre-expand-export' to expand it. There's a corresponding `expand-export' > for provide macros. > > To make a wrapper, use `syntax-local-lift-expression' to lift the syntax > of the wrapper's definition to the module level. You can then export it by > having a pre-provide macro return `(provide wrapper-id)'. > > In dealing with requires and provides, you'll need to deal with phases. > The mysterious "modes" mentioned in the docs on require and provide > transformers are relative phases. I've found the following function helpful > in a few places: > > (define-for-syntax (phases->abs-phases phases) > (map (λ (phase) (and phase (+ phase (syntax-local-phase-level)))) > (if (null? phases) '(0) phases))) > > It turns relative phases into absolute phases, and ensures that there's > always at least one. You'll want this if you want to look up identifiers to > ensure they're defined, or lift a provide (so you can wrap it properly in a > `for-meta'). If you can stick to just syntax transformations in your > provide macros, you won't need it at all - just pass the relative phases > through to `expand-export' and `pre-expand-export'. > > In existing provide macros like `all-from-out', you'll see "(apply append > (map (lambda ...) ...))" in a few places. These map over identifiers and > phases, and collect all the results. I've found "(append* (for/list ...))" > and "(append* (for*/list ...))" are cleaner. (Of course, in "reqprov.rkt", > the `for' macros haven't been defined yet.) > > I think this should be enough to get started on. > > Neil T > ______________________________**___________________ > For list-related administrative tasks: > > http://lists.racket-lang.org/**listinfo/users<http://lists.racket-lang.org/listinfo/users> -- Ismael
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