Re: Enhanced 'warning'

[ludo@gnu.org (Ludovic Courtès)]

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> You should reuse the body of the current ‘warning’ macro, though.
>
> What's wrong with this macro?
>
> (define-syntax define-diagnostic
>   (syntax-rules ()
>     ((define-diagnostic name prefix)

Since there’s a single rule, you should use ‘define-syntax-rule’
instead, for conciseness.

>      (define-syntax name
>        (lambda (x)
>          (define (augmented-format-string fmt)
>            (string-append "~:[~*~;guix ~a: ~]~a" (syntax->datum fmt)))
>
>          (syntax-case x (N_ _)                    ; these are literals, yeah...
>            ((name (_ fmt) args ...)
>             (string? (syntax->datum #'fmt))
>             (with-syntax ((fmt*   (augmented-format-string #'fmt))
>                           (prefix (datum->syntax x prefix)))
>               #'(format (guix-warning-port) (gettext fmt*)
>                         (program-name) (program-name) prefix
>                         args ...)))
>            ((name (N_ singular plural n) args ...)
>             (and (string? (syntax->datum #'singular))
>                  (string? (syntax->datum #'plural)))
>             (with-syntax ((s      (augmented-format-string #'singular))
>                           (p      (augmented-format-string #'plural))
>                           (prefix (datum->syntax x prefix)))
>               #'(format (guix-warning-port)
>                         (ngettext s p n %gettext-domain)
>                         (program-name) (program-name) prefix
>                         args ...)))))))))
>
> I'm getting the "extra ellipsis in form" error.

This is a macro-generating macro.  In the body of the generated macro,
above, there are 4 occurrences of ‘...’.  But these ellipses have no
meaning in the outer macro; they are just meaningful in the context of
the generated macro, hence the error.

Instead, you should replace all 4 occurrences with (... ...).

Yes, it’s always surprising at first.  ;-)

Ludo’.