[Haskell-cafe] is value evaluated?
Brandon S. Allbery KF8NH
allbery at ece.cmu.edu
Fri May 8 12:56:48 EDT 2009
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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