[Haskell-cafe] Re: Laziness question

[Brandon S Allbery KF8NH]

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On 8/2/10 17:18 , Stefan Holdermans wrote:
> Brandon,
>>> h :: (x ~ y, Eval (y -> Int)) => (x -> Int) -> (y -> Int) -> Int
> 
>>  But actually if you push the constraint inward, into the type so to say, you actually get quite close to Janis' and David's solution.
> 
> Sorry, I was thinking out loud there. I meant the Eval constraint, not the equality constraint.  But, right now, I guess my comment only makes sense to me, so let's pretend I kept quiet. ;-)

The point of this discussion is that the Eval constraint needs to be on one
of the functions.  So I tried to specify that (x -> Int) and (y -> Int) are
different types despite x and y being the same type, because one of them has
an Eval constraint.  This may be a shortcoming of Haskell (or System Fc?)
types, although it may be doable with a newtype.

- -- 
brandon s. allbery     [linux,solaris,freebsd,perl]      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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