[debbugs-tracker] bug#14482: closed (Macro not able to see a function)

[GNU bug Tracking System]

Your message dated Thu, 30 May 2013 23:21:59 +0200
with message-id <address@hidden>
and subject line Re: bug#14482: Macro not able to see a function
has caused the debbugs.gnu.org bug report #14482,
regarding Macro not able to see a function
to be marked as done.

(If you believe you have received this mail in error, please contact
address@hidden)


-- 
14482: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14482
GNU Bug Tracking System
Contact address@hidden with problems
> --- Begin Message ---
>
>
>
> Subject: 
>
> Macro not able to see a function
>
>
>
>
> Date: 
>
> Mon, 27 May 2013 12:51:42 +0200
>
>
>
>
> Hi,
>
> Here is example code:
>
> ---------------------------------------
>
> (define (partition-two lst)
>   (if (< (length lst) 2)
>     '()
>     (cons
>       (list (car lst) (cadr lst))
>       (partition-two (cddr lst)))))
>
> (define-macro (letn bindings . body)
>   `(let* ,(partition-two bindings)
>      ,@body))
>
> (define (println v)
>   (display v)
>   (newline))
>
> (println
>   (letn (a 3
>          b 4
>          c 4
>          d a
>          f (+ a b))
>      (+ a b c d f)))
>
> ---------------------------------------
>
> It correctly prints result, but I'm getting also:
>
> ---------------------------------------
> ;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
> ;;;       or pass the --no-auto-compile argument to disable.
> ;;; compiling /home/sanel/letn.ss
> ;;; WARNING: compilation of /home/sanel/letn.ss failed:
> ;;; ERROR: Unbound variable: partition-two
> 21
> ---------------------------------------
>
> I'm using guile: 2.1.0.180-9b977-dirty
>
> Best.
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#14482: Macro not able to see a function
>
>
>
>
> Date: 
>
> Thu, 30 May 2013 23:21:59 +0200
>
>
>
>
> User-agent: 
>
> Gnus/5.130007 (Ma Gnus v0.7) Emacs/24.3 (gnu/linux)
>
>
>
>
> tags 14482 notabug
> thanks
>
> Hi,
>
> Sanel Zukan <address@hidden> skribis:
>
> > ---------------------------------------
> >
> > (define (partition-two lst)
> >   (if (< (length lst) 2)
> >     '()
> >     (cons
> >       (list (car lst) (cadr lst))
> >       (partition-two (cddr lst)))))
> >
> > (define-macro (letn bindings . body)
> >   `(let* ,(partition-two bindings)
> >      ,@body))
> >
> > (define (println v)
> >   (display v)
> >   (newline))
> >
> > (println
> >   (letn (a 3
> >          b 4
> >          c 4
> >          d a
> >          f (+ a b))
> >      (+ a b c d f)))
> >
> > ---------------------------------------
> >
> > It correctly prints result, but I'm getting also:
> >
> > ---------------------------------------
> > ;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
> > ;;;       or pass the --no-auto-compile argument to disable.
> > ;;; compiling /home/sanel/letn.ss
> > ;;; WARNING: compilation of /home/sanel/letn.ss failed:
> > ;;; ERROR: Unbound variable: partition-two
> > 21
> > ---------------------------------------
>
> That’s because ‘partition-two’ is only visible at run time, and not at
> macro-expansion time.
>
> To fix that, use the ‘eval-when’ form:
>
> --8<---------------cut here---------------start------------->8---
> (eval-when (load compile eval)
>    (define (partition-two lst)
>      (if (< (length lst) 2)
>          '()
>          (cons
>           (list (car lst) (cadr lst))
>           (partition-two (cddr lst))))))
> --8<---------------cut here---------------end--------------->8---
>
> (BTW, I recommend looking at R5RS ‘syntax-rules’ and R6RS ‘syntax-case’
> hygienic macros.)
>
> Ludo’.
>
>
> --- End Message ---