Issue: TEST-NOT-IF-NOT (Version 3)

[masinter.pa@Xerox.COM]

I added a summary of the negative comments to the discussion
section.

My intention is to allow people to vote "Yes" "No" or
"Yes if.../No but...". If we get a majority of Yes votes, it 
passes. If we get a majority of No votes, it fails and we won't
bring it up again. If don't get a majority, we'll look at the
Yes if.../No but... conditions and try to come up with a new
set of proposals that satisfy the constraints.

!
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)

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):

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

  Remove 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.
  
Proposal (TEST-NOT-IF-NOT:FLUSH-TEST-NOT):

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

  Rationale:
  
    This makes the language a bit simpler and easier to explain.
  
  Cost to Implementors:
  
    Very slight.
  
    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 both of these 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.