[Haskell-cafe] is value evaluated?

Joe Fredette jfredett at gmail.com
Fri May 8 13:07:57 EDT 2009

That must have been the vibe I was getting. My haskell-spider senses 
were tingling, I just overshot RT and went for the Halting Problem.


Brandon S. Allbery KF8NH wrote:
> On May 8, 2009, at 01:33 , Joe Fredette wrote:
>> That strikes me as being bad in a "I'm violating the Halting Problem" 
>> sort of way- but I'm not sure how. Is there some contradictory 
>> construction that
>> could be built from such a function?
> I don't think it is; surely the Haskell runtime knows which thunks it 
> has evaluated.  It just explicitly violates referential transparency, 
> and therefore must be in IO.  You may be thinking that it would return 
> a result for _|_, but as described if you fed it _|_ it could only 
> produce False (if the _|_ has been evaluated you would not be able to 
> reach the test).
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