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case using other equality-testing predicates
- To: common-lisp@SU-AI.ARPA
- Subject: case using other equality-testing predicates
- From: David A. Moon <Moon@SCRC-STONY-BROOK.ARPA>
- Date: Wed, 21 May 86 14:14 EDT
- In-reply-to: <FAHLMAN.12208349281.BABYL@C.CS.CMU.EDU>
Date: Tue, 20 May 1986 23:45 EDT
From: "Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>
I'm sure some people will jump all over me for suggesting this,
but it might be better to allow CASE to accept a :TEST keyword. Which
of these three syntaxes do you-all prefer?
(selector item equalp ("foo" ...) ...)
(case item :test #'equalp ("foo" ...) ...)
(cond ((equalp item "foo") ...) ...)
I think that mixing keywords into a construct like Case that already has
a complex syntax is likely to cause confusion.
I agree. But the other alternatives cause confusion, too.
I would prefer adding a
new construct CASE-TEST that would look like
(case-test #'equalp item ("foo" ...) ...)
This is similar to your Selector, but without the odd treatment of the
test function, and the name emphasizes the close parallel to Case. I
think it is best to put the test function before the item -- other
things in the language put the testing function first.
So where would additional options, such as :KEY and an option that
controls whether or not the keys at the heads of the clauses are
evaluated, go in your syntax?
I guess it's obvious why Common Lisp doesn't currently have a way to do this
-- no one has thought of a syntax for it that anyone else likes.