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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.c
Subject: Re: else ladders practice
Date: Wed, 6 Nov 2024 07:26:25 -0000 (UTC)
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On 2024-11-05, Bart <bc@freeuk.com> wrote:
> On 05/11/2024 20:33, David Brown wrote:
>> On 05/11/2024 20:39, Waldek Hebisch wrote:
>>> David Brown <david.brown@hesbynett.no> wrote:
>>>> On 05/11/2024 13:42, Waldek Hebisch wrote:
>>>>> Bart <bc@freeuk.com> wrote:
>>>>>>
>>>>>> Then we disagree on what 'multi-way' select might mean. I think it 
>>>>>> means
>>>>>> branching, even if notionally, on one-of-N possible code paths.
>>>>>
>>>>> OK.
>>>>
>>>> I appreciate this is what Bart means by that phrase, but I don't agree
>>>> with it.  I'm not sure if that is covered by "OK" or not!
>>>
>>> You may prefer your own definition, but Bart's is resonable one.
>> 
>> The only argument I can make here is that I have not seen "multi-way 
>> select" as a defined phrase with a particular established meaning.
>
> Well, it started off as 2-way select, meaning constructs like this:
>
>     x = c ? a : b;
>     x := (c | a | b)
>
> Where one of two branches is evaluated. I extended the latter to N-way 
> select:
>
>     x := (n | a, b, c, ... | z)

This looks quite error-prone. You have to count carefully that
the cases match the intended values. If an entry is
inserted, all the remaining ones shift to a higher value.

You've basically taken a case construct and auto-generated
the labels starting from 1.

If that was someone's Lisp macro, I would prefer they confine
it to their own program. :)

1> (defmacro nsel (expr . clauses)
     ^(caseql ,expr ,*[mapcar list 1 clauses]))
nsel
2> (nsel 1 (prinl "one") (prinl "two") (prinl "three"))
"one"
"one"
3> (nsel (+ 1 1) (prinl "one") (prinl "two") (prinl "three"))
"two"
"two"
4> (nsel (+ 1 3) (prinl "one") (prinl "two") (prinl "three"))
nil
5> (nsel (+ 1 2) (prinl "one") (prinl "two") (prinl "three"))
"three"
"three"
nil
6> (macroexpand-1 '(nsel x a b c d))
(caseql x (1 a)
  (2 b) (3 c)
  (4 d))

Yawn ...

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca