Re: Instead of pcase

[Jim Porter]

On 11/20/2023 6:42 PM, Richard Stallman wrote:
> I uderstand that when you say it, but when I saw the line
>
> >           > (`(,hookfun . (,start ,end ,collection . ,plist))
>
> I was not sure which part of the line that rule applies to.
>
> In particular, what is the reason for the period and inner
> parenthsses?  Why doesn't the code say this?
>
> >           > (`(,hookfun ,start ,end ,collection . ,plist)
>
> Would that be equiva;ent?

Yes, These are equivalent (unless I'm severely mistaken):

----------------------------------------

(pcase '(func 0 10 coll plist1 plist2)
  (`(,hookfun . (,start ,end ,collection . ,plist))
   (message "hookfun = %s start = %s end = %s collection = %s plist = %s"
            hookfun start end collection plist)))

 => "hookfun = func start = 0 end = 10 collection = coll plist = 
(plist1 plist2)"


(pcase '(func 0 10 coll plist1 plist2)
  (`(,hookfun ,start ,end ,collection . ,plist)
   (message "hookfun = %s start = %s end = %s collection = %s plist = %s"
            hookfun start end collection plist)))

 => "hookfun = func start = 0 end = 10 collection = coll plist = 
(plist1 plist2)"

----------------------------------------

> I could not assume the inner parenthsses were unnecessary.  Maybe
> there was a conventiob by which they change the meaning.
> I did not know.

I think this might be a case where the 'pcase' code was written in a 
more-cryptic-than-necessary manner, which adds extra confusion. This 
could be a good example to include in some documentation though: it can 
show how one's intuition about "ordinary" backquoted forms can apply 
directly to reading 'pcase'.