Re: Instead of pcase

[Dmitry Gutov]

On 18/11/2023 05:04, Richard Stallman wrote:
>          > (`(,_ . ,(and (pred functionp) f)) (funcall f))
>          > (`(,hookfun . (,start ,end ,collection . ,plist))
>
> I read the Info documentation of pcase a few days ago and I can't
> recall the rules for understanding those two pcase clauses.  What I
> recall is that they are not to be interpreted as Lisp expressions.
> They contain code that looks like Lisp but does not have the same
> semantic rules as Lisp.

Yes: it's a domain-specific language.

To interpret those backquotes and commas, one can imagine that the they 
do the inverse of the usual.

If normally you have commas to insert the values from the environment 
(variables or expressions) into the backquoted form, then inside pcase 
they are used to do the opposite: to extract values from the expression 
at given positions, and bind them with given names in the corresponding 
clause's environment.

I think that's pretty clever, but also quite readable once you "grok" 
the above idea.