-- here's the class we are defining
class Foo a where
    equ :: a -> a -> Bool

-- here are two data types who are members
-- of the class
data Bar = Barc Integer
data Baz = Bazc Double

-- helper methods
ubarc (Barc a) = a
ubazc (Bazc a) = a

-- make Bar an instance of Foo
instance Foo Bar where
    equ a b = (ubarc a) == (ubarc b)

-- make Baz an instance of Foo
instance Foo Baz where
    equ a b = (ubazc a) == (ubazc b)

-- create some data
t1 = Barc 3
t2 = Barc 4
t3 = Bazc 1.0
t4 = Bazc 1.0

main = do
    putStrLn(show(t1 `equ` t2))
    putStrLn(show(t3 `equ` t4))