Re: Question on pcase

[Oleh Krehel <ohwoeowho@gmail.com>]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Oleh Krehel <ohwoeowho@gmail.com> writes:
>
>> Thanks Michael, that's almost exactly what I need. The only thing is
>> that I don't understand what `-bind-' is.
>
> That's just a placeholder I used.  Depending on what pcase form you are
> using (`pcase', `pcase-lambda', `pcase-let'), the semantic is a bit
> different.
>
> You can just imagine that it creates a local binding, like `let', and
> that binding is available in the CODE part of the
>
>   (PATTERN CODE...)
>
> of this branch.
>
> The actual code `pcase' produces is easy as well but longer; when I
> included this aspect in `pcase-demystify-pattern', the result would look
> more like what you would get with `macroexpand', so I don't think it
> would be useful, since the semantic is also slightly different in other
> `pcase' derived macros.

I think there's a bit of miscommunication here. I can `macroexpand' as
well, but the branch info isn't clear-cut in that case.  The thing is
that I don't want to use `pcase-demystify-pattern' to understand
approximately what each pattern does, I want it to expand to the exact
code that is run for a branch, and I want to run that code.

This can all be done in-place without producing extra buffers. A simple
"C-c C-e" on a branch should either:

    (message "the branch doesn't match")

or e.g.:

    (progn
      (setq hookfun (car res))
      (setq start (nth 0 (cdr res)))
      (setq end (nth 1 (cdr res)))
      (setq collection (nth 2 (cdr res)))
      (setq plist (nthcdr 3 (cdr res)))
      (message "match"))

Instead, (pcase-demystify-pattern '`(,hookfun . (,start ,end ,collection . ,plist)))
gives:

    (if (consp -tested-expression-)
        (let* ((x (car -tested-expression-))
               (x (cdr -tested-expression-)))
          (if (consp x)
              (let* ((x (car x))
                     (x (cdr x)))
                (if (consp x)
                    (let* ((x (car x))
                           (x (cdr x)))
                      (if (consp x)
                          (let* ((x (car x))
                                 (x (cdr x)))
                            (progn
                              (-bind- plist x)
                              (-bind- collection x)
                              (-bind- end x)
                              (-bind- start x)
                              (-bind- hookfun x)))
                        nil))
                  nil))
            nil))
      nil)

Which is indeed close to what I need. I guess `-bind-` should be some
macro that pops and does a `set'. I'm just not sure that this is exactly
true, and will work for all patterns.