Re: else ladders practice

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 ...

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