From: Maxime Devos <maximedevos@telenet.be>
To: "Ludovic Courtès" <ludo@gnu.org>, guile-devel@gnu.org
Subject: Re: [PATCH] Print backtraces for syntax errors too.
Date: Sat, 25 Feb 2023 00:38:50 +0100 [thread overview]
Message-ID: <308e0731-1532-b39a-d169-eace8fe30019@telenet.be> (raw)
In-Reply-To: <871qmf2hfb.fsf@gnu.org>
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On 24-02-2023 16:48, Ludovic Courtès wrote:
> Maxime Devos <maximedevos@telenet.be> skribis:
>
>> ;; Before:
>> ;; unknown file:#f:#f: syntax-stuff-twice: bad in subform
>> #<syntax:reproducer.scm:15:27 "imagine this syntax is very hard to
>> follow"> of #<syntax:reproducer.scm:15:27 "imagine this syntax is
>> very hard to follow">
>> ;; After:
>> ;; [the same thing]
>> ;;
>> ;; Looks like another patch is needed ...
>
> What backtrace are you trying to get?
>
> Getting a backtrace showing which macros are being expanded (similar to
> what GCC does) would be great, but it’s much more work; changing this
> one line in libguile won’t achieve that.
Just a regular backtrace like Guile already makes for exceptions
unrelated to syntax, not some kind of expansion backtrace that tracks
macro expansion.
For example, let's say you have a macro that during expansion throws an
exception in some cases. For non-'syntax-error' exception types, a
backtrace is printed:
;; a.scm
(define-module (a) #:export (whatever))
(define (syntax-negate s)
(syntax-case s ()
(#false #true)
(#true #false)
(_ (error "bogus!")))) ; <--- line 6!
(define (syntax-identity s) ; identity
(syntax-case s ()
(#false #'#false)
(#true #'#true)
(_ (error "bogus!"))))
(define-syntax whatever
(lambda (s)
(syntax-case s ()
((_ x) #`(#,(syntax-negate #'x) #,(syntax-identity #'x))))))
;; b.scm
(use-modules (a))
(whatever 0)
;; Shell commands
guild compile a.scm
guild compile -L . b.scm
;; Output: a backtrace that mentions on which line of a.scm things went
wrong:
Backtrace:
[Lots of lines]
In ice-9/psyntax.scm:
[More lines]
In a.scm:
6:7 1 (_ _)
In ice-9/boot-9.scm:
1685:16 0 (raise-exception _ #:continuable? _)
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
bogus!
However, suppose I removed the (_ (error "bogus!")) lines and hence the
code produces syntax-error exceptions:
;; c.scm
(define-module (c) #:export (whatever))
(define (syntax-negate s)
(syntax-case s () ; L3
(#false #true)
(#true #false)))
(define (syntax-identity s) ; identity
(syntax-case s () ; L7
(#false #'#false)
(#true #'#true)))
(define-syntax whatever
(lambda (s)
(syntax-case s ()
((_ x) #`(#,(syntax-negate #'x) #,(syntax-identity #'x))))))
;; d.scm
(use-modules (c))
(whatever 0)
;; Shell commands
guild compile c.scm
guild compile -L . d.scm
;; Output: no backtrace at all!
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Syntax error:
d.scm:2:10: source expression failed to match any pattern in form 0
;; In case of complicated macros, it would be nice if it said _which_
;; pattern matcher failed: L3, or L7, like with a.scm+b.scm.
Summarised, I want the relatively nice backtrace that happens for
non-'syntax-error' exceptions from a.scm+b.scm (*) (it's verbose, has
lots of irrelevant stuff, but ultimately it provides an useful piece of
information: the line number on which a pattern matcher failed).
(*) Ideally you would have both the backtrace _and_ the line number in
b.scm/d.scm.
Greetings,
Maxime.
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prev parent reply other threads:[~2023-02-24 23:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-08 15:59 [PATCH] Print backtraces for syntax errors too Maxime Devos
2023-02-23 11:38 ` Ludovic Courtès
2023-02-23 19:04 ` Maxime Devos
2023-02-23 19:10 ` Maxime Devos
2023-02-23 19:27 ` Maxime Devos
2023-02-24 15:48 ` Ludovic Courtès
2023-02-24 23:38 ` Maxime Devos [this message]
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