On Tue, Dec 20, 2011 at 9:47 PM, Gregory Crosswhite <gcrosswh...@gmail.com>wrote:
> > On Dec 20, 2011, at 8:40 PM, Jesse Schalken wrote: > > If you think a value might not reduce, return an error in an error monad. > > > Okay, I'm completely convinced! Now all that we have to do is to solve > the halting problem to make your solution work... :-) > Why do you have to solve the halting problem? Consider integer division by 0. intDiv x y = if y > x then 0 else 1 + (intDiv (x - y) y) This is correct, but does not reduce with y = 0. The Prelude version returns bottom in this case. Here is a version that returns an error in an Either String. intDiv :: (Ord a, Num a) => a -> a -> Either String a intDiv _ 0 = Left "Division by 0!" intDiv x y = if y > x then Right 0 else intDiv (x - y) y >>= (Right . (1 +)) This is all I was talking about. Cheers, > Greg >
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