At Sat, 12 Feb 2011 23:28:47 -0500, Eli Barzilay wrote: > Using (except-out whatever x) will omit not only `x', but also any > other names that `x' is provided as. For example: > > (module A racket > (define x 1) > (provide x (rename-out [x y]))) > (module B racket > (require 'A) > (provide (except-out (all-from-out 'A) x))) > (module C racket > (require 'B) > y) ; error > > and it goes the other way too (excluding `y' and trying to use `x'). > When I saw this, it seemed familiar so I looked at the docs. My guess > is that this: > > The symbolic export name information in the latter provide-specs is > ignored; only the bindings are used. > > is saying that the above is expected. If so, then it looks like it > should definitely be clarified, maybe move this sentence after the > example, explain the specific (common) case of excluding a name that > was provided with a different name, and also adding an example for > this?
Ok, I'll try to clarify in the docs. > But at a higher level, is there a reason to not look at the name? I think it interacts badly with `require'- and `provide'-generating macros. > It > seems bad in that the two options of > 1. (define x y) (provide x) > 2. (provide (rename-out [y x])) > can lead to a different result, where the second one ties the two > names for this kind of filtering. I'm not sure I understand what you mean. Do you mean that `x' is different from `(rename-out [y x])' when wrapped with `(except-out ... y)'? > It's also weird that the two names > are the same for `except-out' but in an `except-in' they're still > separate. If I'm following, then I think it derives from the difference between bindings and uses and how those interact with macros. A variant of `except-out' that refers to external names instead of internal bindings may be useful, too. > And BTW, it's also surprising that the exceptions are provide-specs, > which makes these: > > (provide (except-out (all-from-out 'A) (rename-out [y foo]))) > (provide (except-out (all-from-out 'A) (prefix-out foo y))) > > be the same as the above. Is this ever useful? I think I've probably used `struct-out' in the second part of `except-out', but that's the only example that comes to mind. _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
