That behavior can be seen as a perversion of IO's behavior—it's roughly known as Lazy IO and is considered convenient but potentially very dangerous. The whole

That behavior can be seen as a perversion of IO's behavior—it's roughly known as Lazy IO and is considered convenient but potentially very dangerous. The whole cottage industry of streaming monadic operators like enumeratees, pipes, conduits, io-streams, etc takes "fixing" Lazy IO as a major design goal or inspiration. Lazy IO depends upon using the function `unsafeInterleaveIO` which, as its name suggests, is considered potentially unsafe---and your example demonstrates why!