My own asdf problem (exactly one of ...)

Hi,

I ran into what I fear is a wall today.  I am working on CLX, and was
attempting to move sbcl implementations of system-independent routines
into their own file, so that where before there was just
"dependent.lisp", there would be "sbcl-dependent.lisp" to be used if
the implementation is sbcl, and "dependent.lisp" otherwise.  The
problem arose when trying to describe this to ASDF.  It's easy enough
to say "don't use sbcl-dependent if :SBCL isn't on *FEATURES*":
  (:module dependent
           (:file "sbcl-dependent"
                  :if-component-dep-fails :try-next
                  :in-order-to ((compile-op (feature :sbcl))))
           ...)
but the description "don't use dependent.lisp if :SBCL *is* on
*FEATURES*" eluded me.  The best I could come up with was
           (:file "dependent"
                  :perform (compile-op :around (o c)
                             (unless (member :sbcl *features*)
                               (call-next-method)))
                  :output-files (compile-op :around (o c)
                                  (unless (member :sbcl *features*)
                                    (call-next-method))))
which did not fill me with joy.  Is there a better way in current
ASDF?  Do other defsystems let you express this in a more consise way?

Cheers,

Christophe
-- 
http://www-jcsu.jesus.cam.ac.uk/~csr21/       +44 1223 510 299/+44 7729 383 757
(set-pprint-dispatch 'number (lambda (s o) (declare (special b)) (format s b)))
(defvar b "~&Just another Lisp hacker~%")    (pprint #36rJesusCollegeCambridge)


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