class  Eq a  where
    (==), (/=)       :: a -> a -> Bool

        -- Minimal complete defintion:
        --      (==) or (/=)
    x /= y           =  not (x == y)
    x == y           =  not (x /= y)

instance Eq Char where

c == c'          =  fromEnum c == fromEnum c'

instance Eq Int where
 
 ...

instance Eq Integer where
   
...

instance Eq Float where
  
...

instance Eq Double where
  
...