Hi Tobias, One thing, that you might want to use instead of :weakly-depends-on is feature dependencies. The syntax is (:feature <feature>) in dependency list, like this: (defsystem #:test :depends-on (#:cl-ppcre (:feature :custom-readtables)) Although, I didn't try it in modules, but I guess, it should work there as well, since the mechanism is generic. Proceed at your own risk... ;) Best, Vsevolod On Thu, Aug 19, 2010 at 11:13 AM, Tobias C Rittweiler <tcr@freebits.de>wrote:
Quite a few libraries come with reader hacks. They usually come with a ENABLE-FOO-SYNTAX function. I'd like those libraries to optionally depend on the named-readtables library, and define a named readtable that includes their hacks. So users can just use (IN-READTABLE FOO:SYNTAX) on a per-file basis.
What do you think would be the best way to do it?
There's :weakly-depends-on which only loads a dependency if that system is present. Named-readtables pushes :NAMED-READTABLE to *FEATURES*. So in principle, people can use
(:weakly-depends-on :named-readtables)
and then
#+named-readtables (named-readtables:defreadtable ...)
Or put that definition in a file readtable.lisp and use feature-conditionalized compilation in the system definition (which used to be, and I guess still is, awfully awkward -- I never remember how to do it.)
Now I'm wondering how good that solution is.
What is if the library was compiled with a core that happened to include named-readtables? Trying to load that fasl with another core file would probably result in an obscure error. Now, it's a shoot-yourself-in-the-foot kind of thing to do, but I'd think it's something that can happen quite easily. Does ASDF somehow guard against this case?
From what I can see, it appears that :WEAKLY-DEPENDS-ON was added in a quick rush thinking that it might be appropriate for conditional compilation, but it really is not. Does that seem true to you, too?
Maybe people can share how they got bitten by it?
I'd think ASDF should include a ./configure step (there are extension for that kind of thing out there), and should then save configuration choices persistently, and check for these when loading a system.
-T.
PS.
Thanks, appreciation, and kudos again to Fare and Robert for having taken up the ASDF hat.
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