On 09/02/07, John Ky
I noticed on Windows that when I use IO functions that write to stdout when the process is lacking a console, those functions throw an IOError. I'm not sure if this also occurs for stderr because I haven't tried it.
This is Windows standard behaviour. For GUI applications, the handles corresponding to std{in,out,err} are not valid, and attempts to write to them give an error. In general, you shouldn't use these handles in a GUI program. Or if you can't guarantee that the libraries you use won't write to them, redirect them to the null device or a log file. (I'm not saying this is ideal behaviour, but that's how it is...)
I believe the most sensible behaviour should be for those functions to not throw, but instead do nothing.
That's not 100% clear - writing to a log file may be better (I don't like the idea of dropping potentially useful information without any warning - and if the output wasn't useful to *someone*, why was it being written?) Annoyingly, Haskell doesn't seem to provide a way to reopen handles (specifically, the standard ones). You may have to use the FFI and the Windows SetStdHandle API to reset the handles. It probably wouldn't be hard to write a reasonably general wrapper for this, but it's a bit late now so I'll leave that as an exercise :-) Paul. Paul.