From: Thien-Thi Nguyen <ttn@gnuvola.org>
To: guile-user@gnu.org
Subject: Re: sxml-match bad pattern syntax
Date: Tue, 28 Dec 2021 02:58:56 -0500 [thread overview]
Message-ID: <87a6gldutb.fsf@gnuvola.org> (raw)
In-Reply-To: <Ycq6aHxHC/pOkRxV@tuxteam.de> (tomas@tuxteam.de's message of "Tue, 28 Dec 2021 08:19:04 +0100")
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() <tomas@tuxteam.de>
() Tue, 28 Dec 2021 08:19:04 +0100
I /think/ the ellipsis is at a wrong place there. Note that
I'm coming from "traditional" match, and I just have wrapped
half of my brain around that (which, BTW, is somewhat painful
:-)
Haha, i know exactly how you feel.
So take this with a grain of salt.
* Phenomenology (aka: I barely know what I'm doing):
If you replace your ellipses above by ". ,rest", things seem
to work:
(define (unbogus x)
(sxml-match x
((a (@ . ,attrs) . ,rest)
`(a (@ ,@(delete '(shape "rect") attrs)) . ,rest))))
(unbogus '(a (@ (shape "rect") (href "foo.html")) "kid"))
=> (a (@ (href "foo.html")) "kid")
Cool. I guest the ". ,rest" is a shortcut for the ellipses.
* Philosophy (aka blah, blah)
If those ellipses resemble what match do, I think they are
wrong there:
(@ . ,attrs) ...
would mean zero or more times the shape "(@ . ,attrs)". I
think this isn't what you want.
Ah, right! The ellipses are a tail that need to follow a head.
I guess i was confused by the documentation's use of ellipses in
the conventional sense rather than the literal sense:
(define (album->html x)
(sxml-match x
[(album (@ (title ,t)) (catalog (num ,n) (fmt ,f)) ...)
`(ul (li ,t)
(li (b ,n) (i ,f)) ...)]))
Anyway, thanks to your help, i've managed to cobble together the
following code, attached here for the benefit of future self:
[-- Attachment #1.2: UNBOGUS --]
[-- Type: text/plain, Size: 559 bytes --]
#!/usr/bin/guile -s
!#
(use-modules
(ice-9 pretty-print)
(sxml match))
(define (pp x)
(pretty-print x)
(newline))
(define (unbogus x)
(sxml-match x
((a (@ . ,attrs) . ,rest)
`(a (@ ,@(delete '(shape "rect") attrs)) . ,rest))
(,otherwise
(if (string? x)
x
`(,(car x) ,(cadr x)
,@(map unbogus (cddr x)))))))
(define one '(a (@ (shape "rect") (href "foo.html")) "kid"))
(newline)
(pp one)
(pp (unbogus one))
(define bad `(p (@) "some text and " ,one " and " ,one))
(newline)
(pp bad)
(pp (unbogus bad))
[-- Attachment #1.3: Type: text/plain, Size: 441 bytes --]
Maybe it's idiomatic. Feedback on how to improve it welcome!
--
Thien-Thi Nguyen -----------------------------------------------
(defun responsep (query) ; (2021) Software Libero
(pcase (context query) ; = Dissenso Etico
(`(technical ,ml) (correctp ml))
...)) 748E A0E8 1CB8 A748 9BFA
--------------------------------------- 6CE4 6703 2224 4C80 7502
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 219 bytes --]
next prev parent reply other threads:[~2021-12-28 7:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-28 6:21 sxml-match bad pattern syntax Thien-Thi Nguyen
2021-12-28 7:19 ` tomas
2021-12-28 7:58 ` Thien-Thi Nguyen [this message]
2021-12-28 8:28 ` tomas
2021-12-28 9:21 ` Thien-Thi Nguyen
2021-12-28 10:06 ` tomas
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