GNU bug report logs - #12216
peek-char incorrectly *CONSUMES* eof

Previous Next

Full log

Message #8 received at 12216 <at> debbugs.gnu.org (full text, mbox):

From: Andy Wingo <wingo <at> pobox.com>
To: dwheeler <at> dwheeler.com
Cc: almkglor <at> gmail.com, 12216 <at> debbugs.gnu.org
Subject: Re: bug#12216: peek-char incorrectly *CONSUMES* eof
Date: Tue, 05 Mar 2013 17:53:45 +0100

Hi,

On Fri 17 Aug 2012 03:53, "David A. Wheeler" <dwheeler <at> dwheeler.com> writes:

> Guile's peek-char has a bug; it incorrectly *consumes* eof instead of
> just reporting it.

I'm not sure there is a sane way to deal with this.  Guile's ports are
fundamentally binary, underneath.  The backing store is a byte buffer
that is decoded and encoded to Scheme characters at need, along with
vtable to fill and flush that buffer.  You can do strange things like
unread characters, switch the encoding, and read them back out in a
different encoding.  There is no way to represent EOF in that buffer.

I have the feeling that for interactive use, if you expect to read a EOF
from a port and then continue, you have to not use peek-char.  You need
to handle your own lookahead buffer.  I know it's not a great answer,
but I can't think of anything else that makes sense.

What do you think?

Andy
-- 
http://wingolog.org/

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.