Yes indeed. 

On Mon, Apr 20, 2009 at 3:42 PM, Jake McArthur <jake.mcarthur@gmail.com> wrote:
Sure, so hnf would give us a non-determined result, but I don't think that makes unamb any less referentially transparent – the same value is always returned, and always reduced at least to hnf.

I think it is hnf that Peter was talking about needing to be in IO, not unamb.

- Jake