[Haskell-cafe] Limits of deduction

[Roberto Zunino]

Matthew Brecknell wrote:

 > Roberto Zunino:
 >
 >>Here passing both 3 and (\z->z) as y confuses the type inference.
 >
 > So the type inference is not really confused at all. It just gives a
 > not-very-useful type.

Yes, you are right, I didn't want to involve type classes and assumed 
3::Int. A better example would be:

polyf :: Int -> a -> Int
polyf x y = if x==0 then 0
             else if x==1 then polyf (x-1) (\z->z)
             else polyf (x-2) ()

Here, passing both () and (\z->z) _does_ make inference fail.

Zun.