[Haskell-cafe] Ready for testing: Unicode support for Handle I/O

[Duncan Coutts]

On Wed, 2009-02-04 at 13:31 +0000, Simon Marlow wrote:
> Duncan Coutts wrote:
> > On Tue, 2009-02-03 at 11:03 -0600, John Goerzen wrote:
> > 
> >> Will there also be something to handle the UTF-16 BOM marker?  I'm not
> >> sure what the best API for that is, since it may or may not be present,
> >> but it should be considered -- and could perhaps help autodetect encoding.
> > 
> > I think someone else mentioned this already, but utf16 (as opposed to
> > utf16be/le) will use the BOM if its present.
> > 
> > I'm not quite sure what happens when you switch encoding, presumably
> > it'll accept and consider a BOM at that point.
> 
> Yes; the utf16 and utf32 encodings accept a BOM (and generate a BOM in 
> write mode).  This caused interesting bugs when doing re-decoding after 
> switching encodings, because the BOM constitutes state in the decoder, 
> which means that decoding is not necessarily repeatable unless you save the 
> state (which iconv doesn't provide a way to do).
> 
> Are there other encodings that have this kind of state?  If so, then they 
> might be restricted to NoBuffering at least when switching encodings.

Yes, I believe there are some Asian encodings that are stateful.

Duncan