From: Maxime Devos <maximedevos@telenet.be>
To: Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>,
Guile User <guile-user@gnu.org>
Subject: Re: Macro for replacing a placeholder in an expression
Date: Thu, 28 Jul 2022 02:55:33 +0200 [thread overview]
Message-ID: <1ede5481-9d46-84e9-2530-d64ac835568b@telenet.be> (raw)
In-Reply-To: <80083c86-19b0-7537-be70-f763bd5b390f@posteo.de>
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These macros all sound more complicated than necessary -- on the first
one, I've sent you a message with sneek:
;; By: Maxime Devos
;; This does not recurse into #(...).
;; Also, such a construct does not nest well, you can't put a replace-result-placeholder inside a replace-result-placeholder meaningfully,
;; so I'm wondering why you're doing this, maybe your goal can be accomplished more robustly with a different method.
(eval-when (expand load eval)
(define (replace-placeholder new code) ; <--- recursively transforms code to replace '<?>' by new
(syntax-case code (<?>)
(<?> new)
((x . y)
#`(#,(replace-placeholder new #'x) . #,(replace-placeholder new #'y)))
(rest #'rest))))
(define-syntax replace-result-placeholder
(lambda (s)
(syntax-case s (<?>) ; <?>: placeholder
((_ new code) (replace-placeholder #'new #'code)))))
(display (replace-result-placeholder
quote
(<?> bar))) ; -> bar
(I think thinking in terms of 'operations' and special-casing lambda etc
would make things harder here)
As a bonus, this supports things like `((x . <?>) (z . w)) which aren't
supported by the original macro as that macro assumed lists.
Greetings,
Maxime.
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next prev parent reply other threads:[~2022-07-28 0:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-27 23:57 Macro for replacing a placeholder in an expression Zelphir Kaltstahl
2022-07-28 0:55 ` Maxime Devos [this message]
2022-07-28 10:23 ` Zelphir Kaltstahl
2022-07-28 10:28 ` Maxime Devos
2022-07-30 15:42 ` Zelphir Kaltstahl
2022-07-30 20:44 ` Maxime Devos
2022-07-30 21:10 ` Maxime Devos
2022-07-30 21:13 ` Maxime Devos
2022-08-05 9:42 ` Linus Björnstam
2022-08-06 14:28 ` Zelphir Kaltstahl
2022-07-28 1:04 ` Maxime Devos
2022-07-28 8:39 ` Zelphir Kaltstahl
2022-07-28 9:48 ` Maxime Devos
2022-07-28 11:26 ` Zelphir Kaltstahl
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