Contents|Symbol Index|Up: Issues|Prev: TAILP-NIL|Next: THE-AMBIGUITY

Cleanup Issue `TEST-NOT-IF-NOT`

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
Category: CHANGE
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 issues: FUNCTION-COMPOSITION

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 (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.

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)