From: Andrew Hyatt <ahyatt@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: pcase defuns
Date: Sun, 19 Dec 2021 16:08:20 -0500 [thread overview]
Message-ID: <m2tuf48fqz.fsf@andrews-mbp.lan> (raw)
In-Reply-To: <jwvv8zka4zc.fsf-monnier+emacs@gnu.org>
On Sun, Dec 19, 2021 at 12:23 PM Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>> As a part of a personal project, I wrote a way to define
>> functions in an equivalent way to pcases. For example:
>>
>> (pcase-defun mytest (a b _)
>> "Match on 'a 'b with the third argument a wildcard" "a b
>> match")
>>
>> (pcase-defun mytest (c ,var _)
>> "Match on 'c binding VAR, with the third argument a wildcard"
>> (format "c %s match" var) )
>>
>> (mytest 'a 'b 'c) -> "a b match" (mytest 'c 100 'c) -> "c 100
>> match"
>>
>> This is all accomplished by a few small but tricky macros and a
>> hashtable that holds all the rules.
>
> This kind of design crossed my mind a few times but I couldn't
> come up with a way to give it a reasonable semantics and
> implementation. Beside the issue of precedence/ordering already
> mentioned by Tassilo, there's the issue of scoping and
> order/timing of macroexpansion. E.g.:
>
> (let ((x 0))
> (pcase-defun mytest (inc-x)
> (setq x (1+ x)))
> (pcase-defun mytest (get-x)
> x))
> (let ((y 0))
> (pcase-defun mytest (inc-y)
> (setq y (1+ y)))
> (pcase-defun mytest (get-y)
> y))
>
> Does this work "right" with your code?
>
> Or:
>
> (eval-when-compile (require 'cl-lib))
>
> (pcase-defun foo (..)
> .. (cl-incf ..) ..)
>
> is `cl-incf` properly macroexpanded during compilation of the
> file, or is it delayed to when the file is loaded, at which
> point the `cl-incf` macro may be undefined?
Great points, thank you! Indeed, both of these wouldn't work - I'm
just quoting and storing the function body for later. I'll have
to think about whether there is something more clever I can do
that would fix these problems.
Does every defun-like thing obey these rules? I'm not familiar
with the range of them, so I'm not sure if this would be violating
convention or not. If so, one thing I can do is to try to
distance this from defun perhaps with a different name such as
`pcase-pattern', and making calls go through a function such as
`pcase-call'.
>
>
> Stefan
next prev parent reply other threads:[~2021-12-19 21:08 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-19 4:53 pcase defuns Andrew Hyatt
2021-12-19 8:34 ` Tassilo Horn
2021-12-19 15:33 ` Andrew Hyatt
2021-12-19 17:16 ` Tassilo Horn
2021-12-19 19:05 ` Stefan Monnier
2021-12-20 5:56 ` Tassilo Horn
2021-12-22 14:07 ` LdBeth
2021-12-19 17:23 ` Stefan Monnier
2021-12-19 21:08 ` Andrew Hyatt [this message]
2021-12-21 4:15 ` Richard Stallman
2021-12-21 5:20 ` Andrew Hyatt
2021-12-22 4:18 ` Richard Stallman
2021-12-23 1:52 ` Andrew Hyatt
2021-12-24 4:13 ` Richard Stallman
2021-12-21 15:32 ` Stefan Monnier
2021-12-20 4:43 ` Richard Stallman
2021-12-23 2:30 ` Po Lu
2022-03-26 17:41 ` Andrew Hyatt
2022-03-27 9:31 ` Stefan Monnier
2022-03-27 18:17 ` Andrew Hyatt
2022-03-28 4:15 ` Richard Stallman
2022-03-30 1:28 ` Andrew Hyatt
2022-03-31 4:27 ` Richard Stallman
2022-04-17 22:09 ` Andrew Hyatt
2022-04-19 3:48 ` Richard Stallman
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