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Re: behavior of CASE with strings PART 2
- From: Per Bothner <per at bothner dot com>
- To: kawa at sourceware dot org
- Date: Tue, 17 Jan 2017 05:23:27 -0800
- Subject: Re: behavior of CASE with strings PART 2
- Authentication-results: sourceware.org; auth=none
- References: <201701171107.25991.Damien.Mattei@unice.fr>
On 01/17/2017 02:07 AM, Damien MATTEI wrote:
testing with eqv? predicate (that seems to be used in kawa CASE if it follow R5RS) and according to https://www.gnu.org/software/kawa/Conditionals.html i have this:
|kawa:1|# (case "dog" (("cat" "dog" "mouse") "animal") (else "mineral or vegetable"))
animal
CASE *cannot* meaningfully be used with strings.
#|kawa:2|# (case (string-copy "dog") (("cat" "dog" "mouse") "animal") (else "mineral or vegetable"))
mineral or vegetable
The reason is that case tests use eqv?, and "The eqv? procedure returns #f if" ...
"obj 1 and obj 2 are pairs, vectors, bytevectors, records,
or strings that denote distinct locations. (quoting directly from R7RS).
R5RS is the same in this respect.
Thus (eqv? (string-copy "dog") "dog") is #f, as is (eqv? (string #\d #\o #\g) "dog").
Even (eqv? "dog" "dog") is *unspecified* according to R7RS, because it does not
require that the two "dog" literals are the same location.
It might be reasonable to add a warning, like Kawa does with lists:
#|kawa:8|# (case "dog" ((("cat") "dog" "mouse") "animal") (else "mineral or vegetable"))
/dev/stdin:8:15: warning - List and vectors will never be matched in a case clause
/dev/stdin:8:15: warning - datum type incompatible with the key
--
--Per Bothner
per@bothner.com http://per.bothner.com/