------------------------------------------------------------------------
module M where
class Seq s a | s -> a where
m :: Seq s b => (a -> b) -> s a -> s b
data PS a = PS String
instance Seq PS Char where
m f (PS s) = PS (map f s)
------------------------------------------------------------------------
This is not accepted by Hugs:
ERROR "M.hs" (line 9): Inferred type is not general enough
*** Expression : m
*** Expected type : (Seq PS Char, Seq PS a) => (Char -> a) -> PS Char -> PS a
*** Inferred type : (Seq PS Char, Seq PS Char) => (Char -> Char) -> PS Char -> PS Char
Is that right? After all, the dependency plus the instance say that
(Seq PS a) implies (a == Char).
BTW. I really miss working functional dependencies in GHC.
--
__("< Marcin Kowalczyk * [EMAIL PROTECTED] http://qrczak.ids.net.pl/
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