CLHS: Issue TEST-NOT-IF-NOT Writeup

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## Issue TEST-NOT-IF-NOT Writeup

    status: Passed, as amended, Jan 89 X3J13
    Note: some confusion in minutes as to whether COMPLEMENT was added
    	as part of TEST-NOT-IF-NOT or whether FUNCTION-COMPOSITION was
    	passed but with only COMPLEMENT preserved.
    	In any case: TEST-NOT-IF-NOT:FLUSH-ALL as stated here
    	passed with "Remove" -> "Deprecate". See issue
    	FUNCTION-COMPOSITION for more details.

    Forum: Cleanup
    Issue:          TEST-NOT-IF-NOT
    References:     Functions offering a :TEST-NOT keyword:
                     ADJOIN (p276), ASSOC (p280), COUNT (p257), DELETE (p254),
                     DELETE-DUPLICATES (p254), FIND (p257),
                     INTERSECTION (p277), MEMBER (p275), MISMATCH (p257),
                     NINTERSECTION (p277), NSET-DIFFERENCE (p278),
                     NSET-EXCLUSIVE-OR (p278), NSUBLIS (p275), NSUBST (p274),
                     NSUBSTITUTE (p256), NUNION (p276), POSITION (p257),
                     RASSOC (p281), REMOVE (p253), REMOVE-DUPLICATES (p254),
                     SEARCH (p258), SET-DIFFERENCE (p278),
                     SET-EXCLUSIVE-OR (p278), SUBLIS (p274), SUBSETP (p279),
                     SUBST (p273), SUBSTITUTE (p255), TREE-EQUAL (p264),
                     UNION (p276);
                    Functions with "-IF-NOT" in their name:
                     ASSOC-IF-NOT (p280), COUNT-IF-NOT (p257),
                     DELETE-IF-NOT (p254), FIND-IF-NOT (p257),
                     MEMBER-IF-NOT (p275), NSUBST-IF-NOT (p274),
                     NSUBSTITUTE-IF-NOT (p256), POSITION-IF-NOT (p257),
                     RASSOC-IF-NOT (p281), REMOVE-IF-NOT (p253),
                     SUBST-IF-NOT (p273), SUBSTITUTE-IF-NOT (p255);
    Related Issue:  FUNCTION-COMPOSITION
    Category:       CHANGE
    Edit history:   02-Oct-88, Version 1 by Pitman (just FLUSH-ALL)
                    05-Oct-88, Version 2 by Pitman (add option FLUSH-TEST-NOT)
                    01-Dec-88, Version 3 by Masinter (add discussion)
                    18-Mar-89, Version 4 by Masinter (as amended)

    Problem Description:

      The -IF-NOT functions are functionally unnecessary.

      The :TEST-NOT keywords are not only functionally unnecessary but
      also problematic because it's not clear what to do when both :TEST
      and :TEST-NOT are provided.

      Many people think Common Lisp is more `bloated' than it needs
      to be and these aspects of the language are commonly cited
      specific examples.

    Proposal (TEST-NOT-IF-NOT:FLUSH-ALL):

      Deprecate all -IF-NOT functions (named above) from Common Lisp.

      Deprecate the :TEST-NOT keyword from the Common Lisp functions which
      currently provide them (named above).

      Rationale:

        This makes the language a bit simpler.

        The removal of :TEST-NOT also makes the language easier to explain.

      Cost to Implementors:

        Very slight.

        Some symbols would disappear from the LISP package but could
        still be offered in proprietary packages if deemed important
        enough.

        Implementations could compatibly retain the :TEST-NOT keywords
        for an interim period.

    Current Practice:

      Presumably no one has done this yet.

    Cost to Users:

      Some rewrites would be needed.

      Those rewrites, which are already fairly simple, would be even
      more simple if some form of the FUNCTION-COMPOSITION issue is
      voted in -- in particular, the COMPLEMENT function which it
      proposes would help enormously in this regard.

    Cost of Non-Adoption:

      Common Lisp would continue to be what some people feel is
      "bigger than it needs to be".

    Benefits:

      The cost of non-adoption would be avoided.

    Aesthetics:

      Presumably this makes the language easier to teach.

    Performance impact:

      Very small; removing the :TEST-NOT keywords would
      make the simple implementation of the functions that
      used to have them slightly faster, but the resulting
      code of the inner loop is likely to be much slower.

    Discussion:

      Many people objected strongly to this proposals --
      they might have been a nice idea five years ago, but are
      gratuitous incompatibilities now: incompatible changes with
      insufficient payback.

      Some of those objections might be tempered if some additional
      changes were made to Common Lisp: adding a COMPLEMENT
      function, or if there were a strategy to declare some parts of the
      language "obsolete". Since these conditions haven't been done,
      their objections stand.

      Steele noted that one main reservation to FLUSH-ALL is that
      he uses REMOVE-IF-NOT much more than REMOVE-IF.

      This issue is related to FUNCTION-COMPOSITION, but is not
      dependent on it.  Some support the combination of  FLUSH-ALL and
      the NEW-FUNCTIONS part of FUNCTION-COMPOSITION in spite of
      the incompatible change because of the aesthetic appeal.

      Some people expressed their intention to vote for FLUSH-ALL
      only if FUNCTION-COMPOSITION:NEW-FUNCTIONS.

      It was noted that and
      adding a #~ readmacro such that
          (FIND-IF-NOT #'ZEROP '(0 0 3))
       == (FIND-IF (COMPLEMENT #'ZEROP) '(0 0 3))
       == (FIND-IF #~ZEROP '(0 0 3))

      The modification of these functions is moot for those who
      prefer to use extended LOOP macro/iteration constructs
      in lieu of the sequence functions.

      Several alternative names for REMOVE-IF-NOT were
      suggested: KEEP-IF, ABSTRACT, FILTER. We did not
      pursue these suggestions.

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