Safe Haskell	Safe
Language	Haskell2010

Data.Strict.Maybe

Description

The strict variant of the standard Haskell Maybe type and the corresponding variants of the functions from Data.Maybe .

Note that in contrast to the standard lazy Maybe type, the strict Maybe type is not an applicative functor, and therefore also not a monad. The problem is the homomorphism law, which states that

pure f <*> pure x = pure (f x)  -- must hold for all f

This law does not hold for the expected applicative functor instance of Maybe , as this instance does not satisfy pure f <*> pure _|_ = pure (f _|_) for f = const .

Synopsis

data Maybe a
- = Nothing
- | Just !a
isJust :: Maybe a -> Bool
isNothing :: Maybe a -> Bool
fromJust :: Maybe a -> a
fromMaybe :: a -> Maybe a -> a
maybe :: b -> (a -> b) -> Maybe a -> b
listToMaybe :: [a] -> Maybe a
maybeToList :: Maybe a -> [a]
catMaybes :: [ Maybe a] -> [a]
mapMaybe :: (a -> Maybe b) -> [a] -> [b]

Documentation

data Maybe a Source #

The type of strict optional values.

Constructors

Nothing
Just !a

Instances

Instances details

Functor Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods fmap :: (a -> b) -> Maybe a -> Maybe b Source # (<$) :: a -> Maybe b -> Maybe a Source #
Foldable Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods fold :: Monoid m => Maybe m -> m Source # foldMap :: Monoid m => (a -> m) -> Maybe a -> m Source # foldMap' :: Monoid m => (a -> m) -> Maybe a -> m Source # foldr :: (a -> b -> b) -> b -> Maybe a -> b Source # foldr' :: (a -> b -> b) -> b -> Maybe a -> b Source # foldl :: (b -> a -> b) -> b -> Maybe a -> b Source # foldl' :: (b -> a -> b) -> b -> Maybe a -> b Source # foldr1 :: (a -> a -> a) -> Maybe a -> a Source # foldl1 :: (a -> a -> a) -> Maybe a -> a Source # toList :: Maybe a -> [a] Source # null :: Maybe a -> Bool Source # length :: Maybe a -> Int Source # elem :: Eq a => a -> Maybe a -> Bool Source # maximum :: Ord a => Maybe a -> a Source # minimum :: Ord a => Maybe a -> a Source # sum :: Num a => Maybe a -> a Source # product :: Num a => Maybe a -> a Source #
Traversable Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods traverse :: Applicative f => (a -> f b) -> Maybe a -> f ( Maybe b) Source # sequenceA :: Applicative f => Maybe (f a) -> f ( Maybe a) Source # mapM :: Monad m => (a -> m b) -> Maybe a -> m ( Maybe b) Source # sequence :: Monad m => Maybe (m a) -> m ( Maybe a) Source #
Eq1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftEq :: (a -> b -> Bool ) -> Maybe a -> Maybe b -> Bool Source #
Ord1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftCompare :: (a -> b -> Ordering ) -> Maybe a -> Maybe b -> Ordering Source #
Read1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftReadsPrec :: ( Int -> ReadS a) -> ReadS [a] -> Int -> ReadS ( Maybe a) Source # liftReadList :: ( Int -> ReadS a) -> ReadS [a] -> ReadS [ Maybe a] Source # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec ( Maybe a) Source # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [ Maybe a] Source #
Show1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftShowsPrec :: ( Int -> a -> ShowS ) -> ([a] -> ShowS ) -> Int -> Maybe a -> ShowS Source # liftShowList :: ( Int -> a -> ShowS ) -> ([a] -> ShowS ) -> [ Maybe a] -> ShowS Source #
NFData1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftRnf :: (a -> ()) -> Maybe a -> () Source #
Hashable1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Methods liftHashWithSalt :: ( Int -> a -> Int ) -> Int -> Maybe a -> Int Source #
Eq a => Eq ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods (==) :: Maybe a -> Maybe a -> Bool Source # (/=) :: Maybe a -> Maybe a -> Bool Source #
Data a => Data ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods gfoldl :: ( forall d b. Data d => c (d -> b) -> d -> c b) -> ( forall g. g -> c g) -> Maybe a -> c ( Maybe a) Source # gunfold :: ( forall b r. Data b => c (b -> r) -> c r) -> ( forall r. r -> c r) -> Constr -> c ( Maybe a) Source # toConstr :: Maybe a -> Constr Source # dataTypeOf :: Maybe a -> DataType Source # dataCast1 :: Typeable t => ( forall d. Data d => c (t d)) -> Maybe0 (c ( Maybe a)) Source # dataCast2 :: Typeable t => ( forall d e. ( Data d, Data e) => c (t d e)) -> Maybe0 (c ( Maybe a)) Source # gmapT :: ( forall b. Data b => b -> b) -> Maybe a -> Maybe a Source # gmapQl :: (r -> r' -> r) -> r -> ( forall d. Data d => d -> r') -> Maybe a -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> ( forall d. Data d => d -> r') -> Maybe a -> r Source # gmapQ :: ( forall d. Data d => d -> u) -> Maybe a -> [u] Source # gmapQi :: Int -> ( forall d. Data d => d -> u) -> Maybe a -> u Source # gmapM :: Monad m => ( forall d. Data d => d -> m d) -> Maybe a -> m ( Maybe a) Source # gmapMp :: MonadPlus m => ( forall d. Data d => d -> m d) -> Maybe a -> m ( Maybe a) Source # gmapMo :: MonadPlus m => ( forall d. Data d => d -> m d) -> Maybe a -> m ( Maybe a) Source #
Ord a => Ord ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods compare :: Maybe a -> Maybe a -> Ordering Source # (<) :: Maybe a -> Maybe a -> Bool Source # (<=) :: Maybe a -> Maybe a -> Bool Source # (>) :: Maybe a -> Maybe a -> Bool Source # (>=) :: Maybe a -> Maybe a -> Bool Source # max :: Maybe a -> Maybe a -> Maybe a Source # min :: Maybe a -> Maybe a -> Maybe a Source #
Read a => Read ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods readsPrec :: Int -> ReadS ( Maybe a) Source # readList :: ReadS [ Maybe a] Source # readPrec :: ReadPrec ( Maybe a) Source # readListPrec :: ReadPrec [ Maybe a] Source #
Show a => Show ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods showsPrec :: Int -> Maybe a -> ShowS Source # show :: Maybe a -> String Source # showList :: [ Maybe a] -> ShowS Source #
Generic ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Associated Types type Rep ( Maybe a) :: Type -> Type Source # Methods from :: Maybe a -> Rep ( Maybe a) x Source # to :: Rep ( Maybe a) x -> Maybe a Source #
Semigroup a => Semigroup ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods (<>) :: Maybe a -> Maybe a -> Maybe a Source # sconcat :: NonEmpty ( Maybe a) -> Maybe a Source # stimes :: Integral b => b -> Maybe a -> Maybe a Source #
Semigroup a => Monoid ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods mempty :: Maybe a Source # mappend :: Maybe a -> Maybe a -> Maybe a Source # mconcat :: [ Maybe a] -> Maybe a Source #
Binary a => Binary ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods put :: Maybe a -> Put Source # get :: Get ( Maybe a) Source # putList :: [ Maybe a] -> Put Source #
NFData a => NFData ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods rnf :: Maybe a -> () Source #
Hashable a => Hashable ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe Methods hashWithSalt :: Int -> Maybe a -> Int Source # hash :: Maybe a -> Int Source #
Generic1 Maybe Source #
Instance details Defined in Data.Strict.Maybe Associated Types type Rep1 Maybe :: k -> Type Source # Methods from1 :: forall (a :: k). Maybe a -> Rep1 Maybe a Source # to1 :: forall (a :: k). Rep1 Maybe a -> Maybe a Source #
Strict ( Maybe a) ( Maybe a) Source #
Instance details Defined in Data.Strict.Classes Methods toStrict :: Maybe0 a -> Maybe a Source # toLazy :: Maybe a -> Maybe0 a Source #
type Rep ( Maybe a) Source #
Instance details Defined in Data.Strict.Maybe type Rep ( Maybe a) = D1 (' MetaData "Maybe" "Data.Strict.Maybe" "strict-0.4.0.1-AAOFHkm4mgeKztrEI4BKIe" ' False ) ( C1 (' MetaCons "Nothing" ' PrefixI ' False ) ( U1 :: Type -> Type ) :+: C1 (' MetaCons "Just" ' PrefixI ' False ) ( S1 (' MetaSel (' Nothing :: Maybe Symbol ) ' NoSourceUnpackedness ' SourceStrict ' DecidedStrict ) ( Rec0 a)))
type Rep1 Maybe Source #
Instance details Defined in Data.Strict.Maybe type Rep1 Maybe = D1 (' MetaData "Maybe" "Data.Strict.Maybe" "strict-0.4.0.1-AAOFHkm4mgeKztrEI4BKIe" ' False ) ( C1 (' MetaCons "Nothing" ' PrefixI ' False ) ( U1 :: Type -> Type ) :+: C1 (' MetaCons "Just" ' PrefixI ' False ) ( S1 (' MetaSel (' Nothing :: Maybe Symbol ) ' NoSourceUnpackedness ' SourceStrict ' DecidedStrict ) Par1 ))

isJust :: Maybe a -> Bool Source #

Yields True iff the argument is of the form Just _ .

isNothing :: Maybe a -> Bool Source #

Yields True iff the argument is Nothing .

fromJust :: Maybe a -> a Source #

Extracts the element out of a Just and throws an error if the argument is Nothing .

fromMaybe :: a -> Maybe a -> a Source #

Given a default value and a Maybe , yield the default value if the Maybe argument is Nothing and extract the value out of the Just otherwise.

maybe :: b -> (a -> b) -> Maybe a -> b Source #

Given a default value, a function and a Maybe value, yields the default value if the Maybe value is Nothing and applies the function to the value stored in the Just otherwise.

listToMaybe :: [a] -> Maybe a Source #

Analogous to listToMaybe in Data.Maybe .

maybeToList :: Maybe a -> [a] Source #

Analogous to maybeToList in Data.Maybe .

catMaybes :: [ Maybe a] -> [a] Source #

Analogous to catMaybes in Data.Maybe .

mapMaybe :: (a -> Maybe b) -> [a] -> [b] Source #

Analogous to mapMaybe in Data.Maybe .