I seem to have some problems understanding preemptive getLine behaviour on cygwin, and wonder whether this is a known/fixed bug/feature (I haven't switched to ghc-6.. yet), or whether anyone has experience with this (behaviour on solaris, with an even older ghc is more or less as expected).
You're running a fairly old version of GHC. With 5.04.3 here I get different behaviour, although strangely it seems that stdin and stdout don't default to LineBuffering in a cygwin shell window.
So that's a third variant of runtime behaviour, then, for the same trivial program (probably cygwin on a more modern windows?)!? What do other GHC versions say? And, more importantly, what _should_ they do? Strangely, with Blockbuffering the program seems to be slightly better behaved than with LineBuffering in cygwin, so the "cat"-hack helps a bit ("strangely", because I'm reading lines, so I'd usually explicitly set LineBuffering.., and "slightly better", because it's still not quite as I would have expected). I'd still like to understand what's going on and how to get my Haskell programs to behave (this arises in a debugging mode of a larger app and means that, at the moment, I can't easily use this for debugging, which makes life slightly difficult, but at least it doesn't seem to cause the bug*..). Cheers, Claus * just checked in an ms-dos-console, which works as expected. So it seems that the issue is an interaction of ghc/cygwin?
Getline LineBuffering 1 "1" 2 "2"