From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Okam <okamsn@protonmail.com>
Cc: 47261@debbugs.gnu.org
Subject: bug#47261: Destructuring with Pcase without assigning values
Date: Fri, 19 Mar 2021 17:45:00 -0400 [thread overview]
Message-ID: <jwvmtuy6crx.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <cc1975f5-4e2f-2a62-5141-062422a754a2@protonmail.com> (Okam's message of "Fri, 19 Mar 2021 13:47:29 +0000")
> For a Pcase pattern, it would be convenient to have Pcase destructure
> the pattern and have a way to see what values Pcase would like to assign
> to variables within the pattern.
>
> This would allow one to know the variables found in the pattern and to
> manipulate the values that Pcase would like to assign, instead of just
> letting `pcase` assign them.
I massaged the code so that it now exports the following function:
(defun pcase-compile-patterns (exp cases)
"Compile the set of patterns in CASES.
EXP is the expression that will be matched against the patterns.
CASES is a list of elements (PAT . CODEGEN)
where CODEGEN is a function that returns the code to use when
PAT matches. That code has to be in the form of a cons cell.
CODEGEN will be called with at least 2 arguments, VARVALS and COUNT.
VARVALS is a list of elements of the form (VAR VAL . RESERVED) where VAR
is a variable bound by the pattern and VAL is a duplicable expression
that returns the value this variable should be bound to.
If the pattern PAT uses `or', CODEGEN may be called multiple times,
in which case it may want to generate the code differently to avoid
a potential code explosion. For this reason the COUNT argument indicates
how many time this CODEGEN is called."
The `pcase` macro itself uses this function, so it should hopefully be
"good enough", but let me know if it's causing you trouble.
Stefan
next prev parent reply other threads:[~2021-03-19 21:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 13:47 bug#47261: Destructuring with Pcase without assigning values Okam via Bug reports for GNU Emacs, the Swiss army knife of text editors
2021-03-19 21:45 ` Stefan Monnier [this message]
2021-04-17 1:24 ` Okam via Bug reports for GNU Emacs, the Swiss army knife of text editors
2021-04-17 3:22 ` Stefan Monnier
[not found] ` <1dacded9-3e40-bc02-56c7-a157d739ffb7@protonmail.com>
2021-04-19 22:06 ` bug#47261: Fwd: " Earl Hyatt via Bug reports for GNU Emacs, the Swiss army knife of text editors
[not found] ` <jwveef84hcl.fsf-monnier+emacs@gnu.org>
[not found] ` <4925d1a5-4669-8290-e534-1662f13ca183@protonmail.com>
2021-04-19 22:10 ` Okam via Bug reports for GNU Emacs, the Swiss army knife of text editors
2022-06-24 18:36 ` Lars Ingebrigtsen
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