References: ASSOC-IF (p280), ASSOC-IF-NOT (p280), RASSOC-IF (p281),
Edit history: 22-Apr-87, Version 1 by Pitman
20-Nov-87, Versions 2,3 by Masinter
23-Nov-87, Version 4 by Masinter
The descriptions of ASSOC-IF, ASSOC-IF-NOT, RASSOC-IF, and RASSOC-IF-NOT do not
mention a :KEY option, although ASSOC and RASSOC have one.
This is often reported as an inconsistency in Common Lisp.
Allow a :KEY keyword for ASSOC-IF, ASSOC-IF-NOT, RASSOC-IF, and RASSOC-IF-NOT.
If not supplied, it should default to #'IDENTITY as do the :KEY keywords for
other -IF and -IF-NOT functions. The function, as with the :KEY argument for
ASSOC and RASSOC, is applied to the CAR of the pair in the association list for
ASSOC-IF and ASSOC-IF-NOT and the CDR of the pair for RASSOC-IF and
A better description of the intent might be to say that the car /contains/ the
key of the association, and by default the car /is/ the key of the association.
(assoc-if #'zerop pathnames :key #'pathname-version)
could be used to search a list indexed by pathnames finding one with zero
This is an inconsistency in the language that is simple to fix.
Symbolics implements :KEY for the -IF and -IF-NOT assoc functions. Others follow
the book and allow :KEY only for ASSOC.
Cost to Common Lisp implementors:
A small amount of additional code is necessary to support this in
implementations not already offering it as an extension.
Cost to Common Lisp users:
The change is essentially upward compatible with user code.
This would make the set of -IF and -IF-NOT functions be more regular in their
All the other -IF and -IF-NOT variations of list operations omit the :TEST and
:TEST-NOT keywords, but allow :KEY. For example, consider the family of MEMBER,
MEMBER-IF, and MEMBER-IF-NOT. Although this introduces additional mechanism, it
does so in a way that probably makes it easier to think about which functions do
what, so it would likely be seen as a simplification.
The omission of :KEY in this situation in CLtL was probably an oversight.
The cleanup committee supports this proposal.