Eq_Instances.lhs

Eq Instances
1.
> data TisAnInteger = TisAn Integer
> instance Eq TisAnInteger where 
>   TisAn n == TisAn n' = n == n'
2. 
> data TwoIntegers = Two Integer Integer
> instance Eq TwoIntegers where 
>   Two n m == Two n' m' = (n == n') && (m == m')
3.
> data StringOrInt = TisAnInt Int | TisAString String
> instance Eq StringOrInt where 
>   TisAnInt n == TisAnInt n' = n == n'
>   TisAString str == TisAString str' = str == str' 
4. 
> data Pair a = Pair a a
> instance Eq a => Eq (Pair a) where 
>   Pair a _ == Pair a' _ = a == a'
5. 
> data Tuple a b = Tuple a b
> instance (Eq a, Eq b) => Eq (Pair a b) where 
>   Tuple a b == Tuple a' b' = (a == a') && (b == b')
6. 
> data Which a = ThisOne a | ThatOne a
> instance Eq a => Eq (Which a) where 
>   ThisOne a == ThisOne a' = a == a' 
>   ThatOne a == ThatOne a' = a == a'
7. 
> data EitherOr a b = Hello a | Goodbye b
> instance (Eq a, Eq b) => Eq (EitherOr a b) where 
>   Hello a == Hello a' = a == a'
>   Goodbye b == Goodbye b' = b == b'