[Haskell-cafe] Optimizing unamb by determining the "state" of a thunk?

[Peter Verswyvelen]

On Mon, Apr 20, 2009 at 10:23 AM, Thomas Davie <tom.davie at gmail.com> wrote:

> Really?  Is it any less referentially transparent than unamb already is -
> i.e. it's referentially transparent, as long as the two values really are
> equal.
>

I think it is. Suppose we call the function hnf :: a -> Bool. hnf might
return a different result for the same argument, since the evaluation of the
argument might be happening on a different thread, so the result of hnf
depends on the time when it is evaluated.  Or am I missing something here?
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