[asdf-devel] [cclan-list] How to depend on a system optionally?
rpgoldman at sift.info
Mon Jul 20 23:39:55 UTC 2009
james anderson wrote:
> On 2009-07-21, at 00:58 , Robert Goldman wrote:
>> Gary King wrote:
>>> I share Robert's queasiness and also think that we want ASDF to
>>> these sorts of dependencies (simple, weak, contingent, etc... (?)).
>>> I'm going to update the manual with James's table (thanks James!)
>>> in the
>>> hopes of giving us a place to hang our collective hats.
>> Follow-on suggestion: we need to think about what happens when a
>> component has all possible combinations of :depends-on,
>> :weakly-depends-on, and :contingent-on. Does something that would not
>> be loaded because of :contingent-on avoid a crash that would come
>> from a
>> violated :depends-on?
> hmmm... depends on what you mean by a "crash".
> it probably does not make sense to define a relation like
> (:file "a" (:contingent-on :osx))
> (:file "b" (:depends-on "a"))
> as that reads as if that "a" will always be present, which is likely
> to cause confusion if the statements are not _real_ close neighbors
> in the system description.
> what does make sense is
> (:module "x"
> (:components ((:module :ffi
> (:components ((:file "a-ffi" (:contingent-on
> "osx" :ccl))
> (:file "a-inter" (:contingent-on "a-
> (:file "b-ffi" (:contingent-on
> "linux" :sbcl))
> (:file "b-inter" (:contingent-on "b-
> (:file "x-ops" (:depends-on :ffi)))
(:file "foobar (:contingent-on (feature :macosx))
It seems like we'd want the :depends-on not to cause an error when
traversing the system if the :contingent-on fails....
What if the weakly-depends-on thing is supposed to establish the feature
we are contingent on?
We probably need to examine the 2^3 combinations here and figure out
what we intend.
>> Extra bonus follow-on: are these expected to be meaningful when the
>> depended-on item is a system (clearly yes), a feature (seems
>> handy), an
>> arbitrary component (what would this mean?)?
> i have used contingent dependencies for all of them.
The current implementation of weakly-depends-on does not work for
anything but a system.
> eg. if a graphics system is to be built somewhere where clx makes
> sense, then there is a system dependency between the graphics package
> and clx.
> in addition, there is a file-level dependency between the clx-based
> implementation of rendering operators and clx's presence.
> one _can_ express everything in terms of #+, but not as clearly.
#+ has different semantics, at least in the asdf-file than your
contingent-on, because the former is resolved more eagerly....
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