Data.Empty

An always empty data structure, i.e. a degenerate container that contains no elements but is aware of the (missing) elements' type, and is a first-class citizen of a number of type classes. E.g. fmapping of any function over Empty is also Empty, two Empty container can be mappended that gives Empty again etc.

Documentation

data Empty a

the empty container

Constructors

Empty

Instances

Monad Empty

Methods

(>>=) :: Empty a -> (a -> Empty b) -> Empty b

(>>) :: Empty a -> Empty b -> Empty b

return :: a -> Empty a

fail :: String -> Empty a

Functor Empty

Methods

fmap :: (a -> b) -> Empty a -> Empty b

(<$) :: a -> Empty b -> Empty a

Applicative Empty

Methods

pure :: a -> Empty a

(<*>) :: Empty (a -> b) -> Empty a -> Empty b

(*>) :: Empty a -> Empty b -> Empty b

(<*) :: Empty a -> Empty b -> Empty a

Foldable Empty

Methods

fold :: Monoid m => Empty m -> m

foldMap :: Monoid m => (a -> m) -> Empty a -> m

foldr :: (a -> b -> b) -> b -> Empty a -> b

foldr' :: (a -> b -> b) -> b -> Empty a -> b

foldl :: (b -> a -> b) -> b -> Empty a -> b

foldl' :: (b -> a -> b) -> b -> Empty a -> b

foldr1 :: (a -> a -> a) -> Empty a -> a

foldl1 :: (a -> a -> a) -> Empty a -> a

toList :: Empty a -> [a]

null :: Empty a -> Bool

length :: Empty a -> Int

elem :: Eq a => a -> Empty a -> Bool

maximum :: Ord a => Empty a -> a

minimum :: Ord a => Empty a -> a

sum :: Num a => Empty a -> a

product :: Num a => Empty a -> a

Traversable Empty

Methods

traverse :: Applicative f => (a -> f b) -> Empty a -> f (Empty b)

sequenceA :: Applicative f => Empty (f a) -> f (Empty a)

mapM :: Monad m => (a -> m b) -> Empty a -> m (Empty b)

sequence :: Monad m => Empty (m a) -> m (Empty a)

Alternative Empty

Methods

empty :: Empty a

(<|>) :: Empty a -> Empty a -> Empty a

some :: Empty a -> Empty [a]

many :: Empty a -> Empty [a]

MonadPlus Empty

Methods

mzero :: Empty a

mplus :: Empty a -> Empty a -> Empty a

Eq (Empty a)

Methods

(==) :: Empty a -> Empty a -> Bool

(/=) :: Empty a -> Empty a -> Bool

Ord (Empty a)

Methods

compare :: Empty a -> Empty a -> Ordering

(<) :: Empty a -> Empty a -> Bool

(<=) :: Empty a -> Empty a -> Bool

(>) :: Empty a -> Empty a -> Bool

(>=) :: Empty a -> Empty a -> Bool

max :: Empty a -> Empty a -> Empty a

min :: Empty a -> Empty a -> Empty a

Monoid (Empty a)

Methods

mempty :: Empty a

mappend :: Empty a -> Empty a -> Empty a

mconcat :: [Empty a] -> Empty a

unwrap :: Empty a -> a

obtain the (missing) value from the container -- always fails