[Haskell-cafe] What unsafeInterleaveIO is unsafe

[Yusaku Hashimoto]

Hello,

I was studying about what unsafeInterleaveIO is.I understood
unsafeInterleaveIO takes an IO action, and delays it. But I couldn't
find any reason why unsafeInterleaveIO is unsafe.

I have already read an example in
http://www.haskell.org/pipermail/haskell-cafe/2009-March/057101.html
says lazy IO may break purity, but I think real matter in this example
are wrong use of seq. did I misread?