17 Apr
2007
17 Apr
'07
1:21 p.m.
Doaitse Swierstra wrote:
Just to show what kind of problems we are currently facing. The following type checks in our EHC compiler and in Hugs, but not in the GHC:
module Test where
data T s = forall x. T (s -> (x -> s) -> (x, s, Int))
run :: (forall s . T s) -> Int run ts = case ts of T g -> let (x,_, b) = g x id in b
Doaitse Swierstra
f :: Double -> (Char -> Double) -> (Char, Double, Int) f double charToDouble = (undefined, double, 0) t :: T Double t = T f -- And what will happen here: run t = ... The "id" in "T g = g _ id" tries to require that f :: Double -> (Double -> Double) -> (Double, Double, Int) but that is not correct.