Control.Empty

Documentation

class HasEmpty f where

The class of type of * -> * which may be empty. There is only one law for HasEmpty and its enforced by the type. The law is that there exists a value in type f for which a is fully generic. This alone is often enough to uniquely determine the value for a given, data type.

Additional laws for HasEmpty work backwards, empty has a relationships with other classes. So if f is a member of one of these classes, the following should hold.

Functor identity

g <$> empty = empty

Applicative annihilation left

x <*> empty = empty

Applicative annihilation right

empty <*> x = empty

Monad identity

empty >>= f = empty

Alternative empty

empty = Alternative.empty

MonadPlus mzero

empty = mzero

Foldable identity

foldr f x empty = empty

Methods

empty :: forall a. f a

empty :: Alternative f => f a

Instances

HasEmpty []

Methods

empty :: [a]

HasEmpty Maybe

Methods

empty :: Maybe a

HasEmpty IO

Methods

empty :: IO a

HasEmpty Option

Methods

empty :: Option a

HasEmpty STM

Methods

empty :: STM a

HasEmpty ReadPrec

Methods

empty :: ReadPrec a

HasEmpty ReadP

Methods

empty :: ReadP a

HasEmpty IntMap

Methods

empty :: IntMap a

HasEmpty Seq

Methods

empty :: Seq a

HasEmpty Set

Methods

empty :: Set a

HasEmpty (Proxy *)

Methods

empty :: Proxy * a

HasEmpty (Map k)

Methods

empty :: Map k a

(Alternative f, Alternative g) => HasEmpty (Product * f g)

Methods

empty :: Product * f g a

(Alternative f, Applicative g) => HasEmpty (Compose * * f g)

Methods

empty :: Compose * * f g a

coerce :: HasEmpty f => a -> f b

isEmpty :: (HasEmpty f, Eq (f a)) => f a -> Bool