[Haskell-cafe] is value evaluated?

[Brandon S. Allbery KF8NH]

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).

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH


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