Re: Block comments and `read-hash-extend'

[ludovic.courtes@laas.fr (Ludovic Courtès)]

The patch below (<87k6kumykq.fsf@laas.fr>) also failed to live through
the summer.  ;-)

Is it acceptable?

Thanks,
Ludovic.

ludovic.courtes@laas.fr (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  <ludovic.courtes@laas.fr>
>
> 	* 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);
>
>
>
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