countable

• class Countable, for countable types

• class AtLeastOneCountable, for countable types that have at least one value

• class InfiniteCountable, for infinite countable types

• class Searchable, for types that can be searched over. This turns out to include some infinite types, see http://math.andrej.com/2007/09/28/seemingly-impossible-functional-programs/.

• class Finite, for finite types

• class Empty, for empty types

• data Nothing, an empty type

Some orphan instances:

• (Searchable a,Eq b) => Eq (a -> b)

• (Finite t) => Foldable ((->) t)

• (Finite a) => Traversable ((->) a)

• (Show a,Finite a,Show b) => Show (a -> b)