Cleanup Issue FUNCTION-COMPOSITION
- Status
- Passed (as amended) Jan 89 X3J13 (And reaffirmed Jun 89 X3J13 that this was the version wanted)
- Forum
- Cleanup
- Category
- ADDITION
- References
- None
- Related issues
TEST-NOT-IF-NOT
Problem Description
A number of useful functions on functions are conspicuously absent from Common Lisp's basic set. Among them are functions which return constant T, constant NIL, and functions which combine functions in common, interesting ways.Proposal (JAN89-X3J13)
Add the following functions:
COMPLEMENT function [Function]
Returns a function whose value is the same as the NOT of the given function applied to the same arguments.
CONSTANTLY value [Function]
Returns a function whose value is always VALUE.
Examples
(MAPCAR #'(LAMBDA (X) (DECLARE (IGNORE X)) T) '(3 A 4.3))
==
(MAPCAR (CONSTANTLY T) '(3 A 4.3))
=> (T T T)
(FIND-IF-NOT #'ZEROP '(0 0 3))
==
(FIND-IF (COMPLEMENT #'ZEROP) '(0 0 3))
=> 3
Rationale
The presence of these functions will contribute to syntactic conciseness in some cases.Current Practice
No Common Lisp implementations provide these functions, but they do exist in the T language.Cost to Implementors
A straightforward implementation is simple to cook up. The definitions given here would suffice. Typically some additional work might be desirable to make these open code in interesting ways.
(DEFUN COMPLEMENT (FUNCTION) #'(LAMBDA (&REST ARGUMENTS) (NOT (APPLY FUNCTION ARGUMENTS))))
(DEFUN CONSTANTLY (VALUE) #'(LAMBDA (&REST ARGUMENTS) (DECLARE (IGNORE ARGUMENTS)) VALUE))
Cost to Users
None. This change is upward compatible.Cost of Non-Adoption
(COMPLEMENT BENEFITS)Benefits
Some code would be more clear. Some compilers might be able to produce better code.
Takes a step toward being able to flush the -IF-NOT functions and the :TEST-NOT keywords, both of which are high on the list of what people are referring to when they say Common Lisp is bloated by too much garbage.
Aesthetics
In situations where these could be used straightforwardly, the alternatives are far less perspicuous.Discussion
Several additional functions (COMPOSE, CONJOIN) were considered and rejected at the Jan 89 X3J13 meeting.Edit History
- 21-Jun-88, Version 1 by Pitman
- 05-Oct-88, Version 2 by Pitman
- 7-Dec-88, Version 3 by Masinter
- 12-Dec-88, Version 4 by Masinter (additional comments)
- 10-Feb-89, Version 5 (as amended by X3J13 Jan 89)