Hi,

I'm trying to get the following code to compile:

=======  Main.hs ==========

import IO

data MyInt = MyInt Int
data MyString = MyString String deriving Show

class Show b => MyClass a b where
    fn :: a -> b

instance MyClass MyInt MyString where
    fn (MyInt i) = MyString (show i)

myprint :: (MyClass a b) => a -> IO ()
myprint a = putStrLn $ show (fn a)

main = myprint 3

=======  Main.hs ==========

with ghc Main.hs -XMultiParamTypeClasses. However, the compiler cannot deduce the type of the b type variable (which in this case is MyString). How can I explicitly tell this information to the compiler?

Many thanks,
Alex.