[Haskell-cafe] What unsafeInterleaveIO is unsafe

[Jake McArthur]

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Yusaku Hashimoto wrote:
| 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 think it depends on what we want to take "unsafe" to mean. In my
opinion, the word "unsafe" should really only be used in cases where
using the function can case an otherwise well-typed program to not be
well-typed. I'm pretty sure I haven't yet seen a case where this applies
to unsafeInterleaveIO.

The biggest problem with unsafeInterleaveIO is that it complicates the
semantics of the IO monad.

- - Jake
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