unofficial mirror of guile-user@gnu.org 
 help / color / mirror / Atom feed
From: "Linus Björnstam" <linus.internet@fastmail.se>
To: "Damien Mattei" <damien.mattei@gmail.com>,
	guile-user <guile-user@gnu.org>
Subject: Re: strange error message in macro
Date: Thu, 01 Jul 2021 10:02:23 +0200	[thread overview]
Message-ID: <939e760a-dfd3-41df-97e8-728c49121b27@www.fastmail.com> (raw)
In-Reply-To: <CADEOade_WNp2jNc13V=WSEfZLWZ7+rYOFtp0Nbw2o=uesxotAQ@mail.gmail.com>

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
> 



      reply	other threads:[~2021-07-01  8:02 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-01  7:34 strange error message in macro Damien Mattei
2021-07-01  8:02 ` Linus Björnstam [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://www.gnu.org/software/guile/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=939e760a-dfd3-41df-97e8-728c49121b27@www.fastmail.com \
    --to=linus.internet@fastmail.se \
    --cc=damien.mattei@gmail.com \
    --cc=guile-user@gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).