From: "Ludovic Courtès" <ludo@gnu.org>
To: guile-user@gnu.org
Subject: Re: syntax taste: use of unquote in macros
Date: Tue, 31 Mar 2020 18:56:17 +0200 [thread overview]
Message-ID: <87imiktqdq.fsf@gnu.org> (raw)
In-Reply-To: dd403a66-123b-2855-39cb-7b5c5f36cd9a@gmail.com
Hi Matt,
Matt Wette <matt.wette@gmail.com> skribis:
> I'm not sure if you know about this, but there is a discrepancy in the
> way some folks define macros to use unquote (aka ,). For example,
>
>> (use-modules (system base pmatch))
>> (pmatch '(foo "bar") ((foo ,val) (write val) (newline)))
> => "bar"
>
>> (use-modules (ice-9 match))
>> (match '(foo "bar") (`(foo ,val) (write val) (newline)))
> => "bar"
>
> Note the difference in the use of quasiquote (aka `) in the pattern
> for (foo ,val): match syntax uses it, pmatch does not.
> In Scheme, quasiquote and unquote always come together.
>
> Is pmatch syntax in bad taste? I'm looking for opinions.
It really depends on what you’re going to use the pattern matcher for.
For ‘sxml-match’, it’s more convenient to have literals be the default
because there are usually more literals than variables, as in:
(sxml-match x
((album (@ (title ,t)) (catalog (num ,n) (fmt ,f)) ...)
`(ul (li ,t)
(li (b ,n) (i ,f)) ...)))
In more general cases, I prefer the (ice-9 match) style because patterns
typically have more variables than literals.
In one case, I found myself implementing pmatch-style quoting on top of
(ice-9 match) so I would have the best of both worlds:
https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/installer/tests.scm#n84
:-)
Ludo’.
prev parent reply other threads:[~2020-03-31 16:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-29 15:11 syntax taste: use of unquote in macros Matt Wette
2020-03-29 22:07 ` Zelphir Kaltstahl
2020-03-30 10:34 ` tomas
2020-03-30 23:43 ` Matt Wette
2020-03-31 9:19 ` tomas
2020-03-30 13:07 ` Arne Babenhauserheide
2020-03-31 16:56 ` Ludovic Courtès [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/guile/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87imiktqdq.fsf@gnu.org \
--to=ludo@gnu.org \
--cc=guile-user@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).