[r6rs] #\x0 is a perfectly valid character datum representation

[r6rs] #\x0 is a perfectly valid character datum representation

[Marco Maggi]

The following R6RS program:

(import (rnrs))

#\x0

fails with:

;;; note: source file proof.sps
;;;       newer than compiled /home/marco/.cache/guile/ccache/2.0-0.R-LE-4/home/marco/var/tmp/proof.sps.go
Backtrace:
In ice-9/boot-9.scm:
 170: 10 [catch #t #<catch-closure 96b6610> ...]
In unknown file:
   ?: 9 [catch-closure]
In ice-9/boot-9.scm:
  62: 8 [call-with-prompt prompt0 ...]
In ice-9/eval.scm:
 389: 7 [eval # #]
In ice-9/boot-9.scm:
1858: 6 [save-module-excursion #<procedure 9758840 at ice-9/boot-9.scm:1871:3 ()>]
1149: 5 [load "proof.sps" #f]
1051: 4 [%start-stack load-stack ...]
1056: 3 [#<procedure 97587b0 ()>]
In unknown file:
   ?: 2 [primitive-load "proof.sps"]
In ice-9/boot-9.scm:
 115: 1 [#<procedure 95aa2f8 at ice-9/boot-9.scm:109:6 (thrown-k . args)> read-error ...]
In unknown file:
   ?: 0 [catch-closure read-error "scm_lreadr" ...]

ERROR: In procedure scm_lreadr:
ERROR: proof.sps:5:5: unknown character name x0

on       a        i686-pc-linux-gnu       using       commit
8d10ccae79ff46f0ebea92ba36acfaebafba8d86.

  It  looks like  the  hex notation  for  characters is  not
recognised by the reader.
-- 
Marco Maggi

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Andy Wingo]

On Mon 21 Jun 2010 10:12, Marco Maggi <marco.maggi-ipsu@poste.it> writes:

> #\x0

Add (read-enable 'r6rs-hex-escapes) to your guile init file.

Mike: is there a more sensible default than the one we have?

Thanks,

Andy
-- 
http://wingolog.org/

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Mike Gran]

> From: Andy Wingo wingo@pobox.com

>> #\x0

> Add (read-enable 'r6rs-hex-escapes) to your 
> guile init file.

> Mike: is there a more sensible default than the one we 
> have?

The idea behind not enabling it by default is because the
r6rs *string* escapes are not backwards compatible with
the hex escapes used with Guile 1.8.x.

"Hello \x57orld" vs "Hello \x57;orld"

There is no perfect way to have both Guile 1.8.x and r6rs
*string* hex escapes at the same time.  You could hack something
together, but, there would be corner cases where it
might be invalid. That's why it was made a reader option.

But, r6rs hex *character* escapes and Guile 1.8.x octal
character escapes could logically coexist without confusion.

But, it might be confusing to have r6rs hex character escapes
that work by default while r6rs string escapes don't work by 
default.

Thanks,

Mike

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Andy Wingo]

Hi Mike,

Thanks for the explanation :-)

On Mon 21 Jun 2010 22:27, Mike Gran <spk121@yahoo.com> writes:

> r6rs hex *character* escapes and Guile 1.8.x octal character escapes
> could logically coexist without confusion.

Let's do that. Shall you, or shall I?

> But, it might be confusing to have r6rs hex character escapes
> that work by default while r6rs string escapes don't work by 
> default.

Well, we'll document this then, and perhaps revisit this in a couple
years.

Andy
-- 
http://wingolog.org/

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Mike Gran]

> From: Andy Wingo wingo@pobox.com

> Hi Mike,

> Thanks for the explanation :-)

>> r6rs hex *character* escapes and Guile 1.8.x octal
>> character escapes could logically coexist without confusion.

> Let's do that. Shall you, or shall I?

It would happen more quickly if you did it.

You'd just have to remove the SCM_R6RS_ESCAPES_P
from the following line of scm_read_character() in read.c

969  if (cp == 'x' && (charname_len > 1) && SCM_R6RS_ESCAPES_P)

Thanks,

Mike

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Mike Gran]

> >> r6rs hex  *character* escapes and Guile 1.8.x octal

> >> character escapes could  logically coexist without confusion.
> 
> > Let's do that. Shall you, or  shall I?

I pushed this change into git.

Thanks,

Mike

Re: [r6rs] #\x0 is a perfectly valid character datum representation

[Andy Wingo]

Hi,

On Sat 17 Jul 2010 13:22, Mike Gran <spk121@yahoo.com> writes:

>> >> r6rs hex  *character* escapes and Guile 1.8.x octal
>
>> >> character escapes could  logically coexist without confusion.
>> 
>> > Let's do that. Shall you, or  shall I?
>
> I pushed this change into git.

Thanks a lot!

Andy
-- 
http://wingolog.org/