Re: Instead of pcase

[Philip Kaludercic <philipk@posteo.net>]

"T.V Raman" <raman@google.com> writes:

> when-let let-alist etc have worked well for me.
>
> What threw me with pcase is there are lots of special chars in that
> particular example whose meaning I dont know, and looking those up and
> understanding their use at the same time was what chased me away

Taking the concrete example you mentioned, 

    (pcase res
      (`(,_ . ,(and (pred functionp) f)) (funcall f))
      (`(,hookfun . (,start ,end ,collection . ,plist))

the unknown or unfamiliar characters are "`" and ",".  The (dynamic)
pcase documentation string is pretty straightforward in explaining what
it does, or can you recall what confused you?:

--8<---------------cut here---------------start------------->8---
-- `QPAT

Backquote-style pcase patterns: `QPAT
QPAT can take the following forms:
  (QPAT1 . QPAT2)       matches if QPAT1 matches the car and QPAT2 the cdr.
  [QPAT1 QPAT2..QPATn]  matches a vector of length n and QPAT1..QPATn match
                           its 0..(n-1)th elements, respectively.
  ,PAT                  matches if the ‘pcase’ pattern PAT matches.
  SYMBOL                matches if EXPVAL is ‘equal’ to SYMBOL.
  KEYWORD               likewise for KEYWORD.
  NUMBER                likewise for NUMBER.
  STRING                likewise for STRING.

The list or vector QPAT is a template.  The predicate formed
by a backquote-style pattern is a combination of those
formed by any sub-patterns, wrapped in a top-level condition:
EXPVAL must be "congruent" with the template.  For example:

  `(technical ,forum)
--8<---------------cut here---------------end--------------->8---

Or if you mean "_", then

--8<---------------cut here---------------start------------->8---
                  PATTERN can take one of the forms:

  _                matches anything.
--8<---------------cut here---------------end--------------->8---

which is familiar to people coming from functional languages, but even
Elisp uses underscores to denote unused variables.