[Haskell-cafe] Re: [Haskell] Lazy IO breaks purity

Gregg Reynolds dev at mobileink.com
Thu Mar 5 12:45:38 EST 2009

On Thu, Mar 5, 2009 at 7:08 AM, Simon Marlow <marlowsd at gmail.com> wrote:

> So the argument is something like: we can think of the result of a call to
> unsafeInterleaveIO as having been chosen at the time we called
> unsafeInterleaveIO, rather than when its result is actually evaluated. This
> is on dodgy ground, IMO: either you admit that the IO monad contains an
> Oracle, or you admit it can time-travel.   I don't believe in either of
> those things :-)
Surely there's a quantum mechanical metaphor waiting to happen here.

   getCat ::  IO Cat

If "getCat" appears in a program text, does it denote or not?  Or both?  If
it does, is the cat alive or dead? (Apologies to

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