On 24-02-2023 16:48, Ludovic Courtès wrote:
Maxime Devos <maximede...@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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