From: Arne Babenhauserheide <arne_bab@web.de>
To: Matt Wette <matt.wette@gmail.com>
Cc: guile-user@gnu.org
Subject: Re: syntax taste: use of unquote in macros
Date: Mon, 30 Mar 2020 15:07:36 +0200 [thread overview]
Message-ID: <87sghqat47.fsf@web.de> (raw)
In-Reply-To: <dd403a66-123b-2855-39cb-7b5c5f36cd9a@gmail.com>
Matt Wette <matt.wette@gmail.com> writes:
> Hi All,
>
> 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.
I did not know about pmatch, but it gives me the feeling that this is a
pattern that will appear again for other embedded domain specific
languages.
I had a usecase for that in dryads-wake¹ for embedding instructions in
otherwise declarative code. It looks like this:
(Enter (Speaker))
(Speaker
(My Text, line 1)
(Second line)
(very ,(color 'red) important ,(color #f) line))
At this point the difference to quasiquote doesn’t look big. It gets
much bigger when this code is used from wisp:²
Enter : Speaker
Speaker
My Text, line 1
Second line
very ,(color 'red) important ,(color #f) line
With written quasiquote there would either be line-noise on every line
or this would have structure-noise because it would have to be wrapped
in a list instead of working like arguments to a procedure call:
(Enter (Speaker))
(Speaker
`((My Text, line 1)
(Second line)
(very ,(color 'red) important ,(color #f) line)))
or
(Enter (Speaker))
(Speaker
`(My Text, line 1)
`(Second line)
`(very ,(color 'red) important ,(color #f) line))
Best wishes,
Arne
¹: https://hg.sr.ht/~arnebab/dryads-wake/browse/default/dryads-wake.w#L231
²: https://www.draketo.de/english/wisp
--
Unpolitisch sein
heißt politisch sein
ohne es zu merken
next prev parent reply other threads:[~2020-03-30 13:07 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 [this message]
2020-03-31 16:56 ` Ludovic Courtès
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