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* strange error message in macro
@ 2021-07-01  7:34 Damien Mattei
  2021-07-01  8:02 ` Linus Björnstam
  0 siblings, 1 reply; 2+ messages in thread
From: Damien Mattei @ 2021-07-01  7:34 UTC (permalink / raw)
  To: guile-user

hello,
'begin' complains of 'sequence of zero expressions in form (begin)'
in:
scheme@(guile-user)> ($  {x <- 7} {y <- 8} (+ x y))
While compiling expression:
Syntax error:
unknown file:2:0: sequence of zero expressions in form (begin)
but:
scheme@(guile-user)> (begin )
make no error !
basically $ is a sort of begin macro that call :
(define-syntax %parse-assignment
  (syntax-rules ()
...

if i wrote:
(define-syntax %parse-assignment
  (syntax-rules (<-)
there is no more error:
scheme@(guile-user)> ($  {x <- 7} {y <- 8} (+ x y))
;;; <stdin>:5:0: warning: possibly unbound variable `x'
;;; <stdin>:5:0: warning: possibly unbound variable `y'
15
result is 15 and good!

i think that the explanation is with syntax-rules parameters not with
begin that would not accept zero expression in form , so why this strange
message?
i suppose i have trouble understanding the behavior and use of syntax-rules
parameters anyway and can not find any reliable documentation about it.

Damien


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: strange error message in macro
  2021-07-01  7:34 strange error message in macro Damien Mattei
@ 2021-07-01  8:02 ` Linus Björnstam
  0 siblings, 0 replies; 2+ messages in thread
From: Linus Björnstam @ 2021-07-01  8:02 UTC (permalink / raw)
  To: Damien Mattei, guile-user

Begin in a Body is spliced into the body. Begin as an expression chain is not spliced, and needs at least one expression.

So: begin in definition context (directly in function bodies and at top-level) can have 0 expressions. Begin in other contexts must have at least one expression.

-- 
  Linus Björnstam

On Thu, 1 Jul 2021, at 09:34, Damien Mattei wrote:
> hello,
> 'begin' complains of 'sequence of zero expressions in form (begin)'
> in:
> scheme@(guile-user)> ($  {x <- 7} {y <- 8} (+ x y))
> While compiling expression:
> Syntax error:
> unknown file:2:0: sequence of zero expressions in form (begin)
> but:
> scheme@(guile-user)> (begin )
> make no error !
> basically $ is a sort of begin macro that call :
> (define-syntax %parse-assignment
>   (syntax-rules ()
> ...
> 
> if i wrote:
> (define-syntax %parse-assignment
>   (syntax-rules (<-)
> there is no more error:
> scheme@(guile-user)> ($  {x <- 7} {y <- 8} (+ x y))
> ;;; <stdin>:5:0: warning: possibly unbound variable `x'
> ;;; <stdin>:5:0: warning: possibly unbound variable `y'
> 15
> result is 15 and good!
> 
> i think that the explanation is with syntax-rules parameters not with
> begin that would not accept zero expression in form , so why this strange
> message?
> i suppose i have trouble understanding the behavior and use of syntax-rules
> parameters anyway and can not find any reliable documentation about it.
> 
> Damien
> 



^ permalink raw reply	[flat|nested] 2+ messages in thread

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