Typeclasses in Haskell

Think of Java Interfaces. A typeclass defines behavior that all members of the typeclass must adhere to.

For example, all instances of the Eq typeclass must implement the == method.

Eq is declared as follows:

class Eq a where
    (==) :: a -> a -> bool

This says that a type a is an instance of Eq if it implements the method == with the given type.