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Re: Block comments and `read-hash-extend'
From: |
Ludovic Courtès |
Subject: |
Re: Block comments and `read-hash-extend' |
Date: |
Fri, 19 Aug 2005 10:11:05 +0200 |
User-agent: |
Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) |
The patch below (<address@hidden>) also failed to live through
the summer. ;-)
Is it acceptable?
Thanks,
Ludovic.
address@hidden (Ludovic Courtès) writes:
> Hi,
>
> The patch below (1) fixes `#! ... !#' block comments and (2) allows to
> override them with `read-hash-extend'.
>
>
> (1) This example makes Guile 1.6 and the current Guile 1.7 hang (for
> some reason which I did not track down):
>
> guile> #! this is a comment !# (+ 2 2)
> [wait forever]
>
> Once the patch is applied:
>
> guile> #! this is a comment !# (+ 2 2)
> 4
>
> I guess block comments have not been widely used over the past
> years. ;-)
>
>
> (2) It makes it possible to discard the block comment syntax with
> `read-hash-extend'. The example below allows to recognize the
> DSSSL keyword syntax[*], at the expense of losing the block
> comment syntax:
>
> (read-hash-extend #\! (lambda (chr port)
> (symbol->keyword (read port))))
>
> I find this particular example useful since, even if DSSSL is
> apparently not widely used, other Scheme implementations such as
> Bigloo do support this syntax, and allowing such extensions is what
> `read-hash-extend' is for.
>
>
> Comments?
>
> Thanks,
> Ludovic.
>
> [*] http://www.ibiblio.org/pub/sun-info/standards/dsssl/dssslo/do960816.htm
>
>
> 2005-06-16 Ludovic Courtès <address@hidden>
>
> * read.c (scm_flush_ws): Do not handle `#! .. !#' block
> comments here so that the behavior of `#!' can be extended with
> `read-hash-extend'.
> (scm_lreadr): Handle the `#!' case here instead of in
> `scm_flush_ws ()' after making sure that no hash reader
> extension exists for `!'. Jump to `tryagain' after call to
> `skip_scsh_block_comment ()', which fixes a bug in block
> comments handling (where Guile would hang).
>
>
>
> Index: read.c
> ===================================================================
> RCS file: /cvsroot/guile/guile/guile-core/libguile/read.c,v
> retrieving revision 1.117
> diff -u -B -b -p -r1.117 read.c
> --- read.c 23 May 2005 19:57:21 -0000 1.117
> +++ read.c 16 Jun 2005 09:13:28 -0000
> @@ -227,9 +227,6 @@ scm_flush_ws (SCM port, const char *eofe
> case EOF:
> eoferr = "read_sharp";
> goto goteof;
> - case '!':
> - skip_scsh_block_comment (port);
> - break;
> default:
> scm_ungetc (c, port);
> return '#';
> @@ -478,9 +475,10 @@ scm_lreadr (SCM *tok_buf, SCM port, SCM
> goto num;
>
> case '!':
> - /* should never happen, #!...!# block comments are skipped
> - over in scm_flush_ws. */
> - abort ();
> + /* Only handle `#! ... !#' block comments if no user extension was
> + defined for `!' using `read-hash-extend'. */
> + skip_scsh_block_comment (port);
> + goto tryagain;
>
> case '*':
> j = scm_read_token (c, tok_buf, port, 0);
>
>
>
> _______________________________________________
> Guile-devel mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/guile-devel
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