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 #

The type of strict optional values.

Constructors

Nothing
Just !a

Instances

Instances details

Functor Maybe #
Instance details Defined in Data.Strict.Maybe Methods fmap :: (a -> b) -> Maybe a -> Maybe b # (<$) :: a -> Maybe b -> Maybe a #
Foldable Maybe #
Instance details Defined in Data.Strict.Maybe Methods fold :: Monoid m => Maybe m -> m # foldMap :: Monoid m => (a -> m) -> Maybe a -> m # foldMap' :: Monoid m => (a -> m) -> Maybe a -> m # foldr :: (a -> b -> b) -> b -> Maybe a -> b # foldr' :: (a -> b -> b) -> b -> Maybe a -> b # foldl :: (b -> a -> b) -> b -> Maybe a -> b # foldl' :: (b -> a -> b) -> b -> Maybe a -> b # foldr1 :: (a -> a -> a) -> Maybe a -> a # foldl1 :: (a -> a -> a) -> Maybe a -> a # toList :: Maybe a -> [a] # null :: Maybe a -> Bool # length :: Maybe a -> Int # elem :: Eq a => a -> Maybe a -> Bool # maximum :: Ord a => Maybe a -> a # minimum :: Ord a => Maybe a -> a # sum :: Num a => Maybe a -> a # product :: Num a => Maybe a -> a #
Traversable Maybe #
Instance details Defined in Data.Strict.Maybe Methods traverse :: Applicative f => (a -> f b) -> Maybe a -> f (Maybe b) # sequenceA :: Applicative f => Maybe (f a) -> f (Maybe a) # mapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b) # sequence :: Monad m => Maybe (m a) -> m (Maybe a) #
Eq1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftEq :: (a -> b -> Bool) -> Maybe a -> Maybe b -> Bool #
Ord1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftCompare :: (a -> b -> Ordering) -> Maybe a -> Maybe b -> Ordering #
Read1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Maybe a) # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Maybe a] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Maybe a) # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Maybe a] #
Show1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Maybe a -> ShowS # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Maybe a] -> ShowS #
NFData1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftRnf :: (a -> ()) -> Maybe a -> () #
Hashable1 Maybe #
Instance details Defined in Data.Strict.Maybe Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Maybe a -> Int #
Eq a => Eq (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods (==) :: Maybe a -> Maybe a -> Bool # (/=) :: Maybe a -> Maybe a -> Bool #
Data a => Data (Maybe a) #
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) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Maybe a) # toConstr :: Maybe a -> Constr # dataTypeOf :: Maybe a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe0 (c (Maybe a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe0 (c (Maybe a)) # gmapT :: (forall b. Data b => b -> b) -> Maybe a -> Maybe a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Maybe a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Maybe a -> r # gmapQ :: (forall d. Data d => d -> u) -> Maybe a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Maybe a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Maybe a -> m (Maybe a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Maybe a -> m (Maybe a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Maybe a -> m (Maybe a) #
Ord a => Ord (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods compare :: Maybe a -> Maybe a -> Ordering # (<) :: Maybe a -> Maybe a -> Bool # (<=) :: Maybe a -> Maybe a -> Bool # (>) :: Maybe a -> Maybe a -> Bool # (>=) :: Maybe a -> Maybe a -> Bool # max :: Maybe a -> Maybe a -> Maybe a # min :: Maybe a -> Maybe a -> Maybe a #
Read a => Read (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods readsPrec :: Int -> ReadS (Maybe a) # readList :: ReadS [Maybe a] # readPrec :: ReadPrec (Maybe a) # readListPrec :: ReadPrec [Maybe a] #
Show a => Show (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods showsPrec :: Int -> Maybe a -> ShowS # show :: Maybe a -> String # showList :: [Maybe a] -> ShowS #
Generic (Maybe a) #
Instance details Defined in Data.Strict.Maybe Associated Types type Rep (Maybe a) :: Type -> Type # Methods from :: Maybe a -> Rep (Maybe a) x # to :: Rep (Maybe a) x -> Maybe a #
Semigroup a => Semigroup (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods (<>) :: Maybe a -> Maybe a -> Maybe a # sconcat :: NonEmpty (Maybe a) -> Maybe a # stimes :: Integral b => b -> Maybe a -> Maybe a #
Semigroup a => Monoid (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods mempty :: Maybe a # mappend :: Maybe a -> Maybe a -> Maybe a # mconcat :: [Maybe a] -> Maybe a #
Binary a => Binary (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods put :: Maybe a -> Put # get :: Get (Maybe a) # putList :: [Maybe a] -> Put #
NFData a => NFData (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods rnf :: Maybe a -> () #
Hashable a => Hashable (Maybe a) #
Instance details Defined in Data.Strict.Maybe Methods hashWithSalt :: Int -> Maybe a -> Int # hash :: Maybe a -> Int #
Generic1 Maybe #
Instance details Defined in Data.Strict.Maybe Associated Types type Rep1 Maybe :: k -> Type # Methods from1 :: forall (a :: k). Maybe a -> Rep1 Maybe a # to1 :: forall (a :: k). Rep1 Maybe a -> Maybe a #
Strict (Maybe a) (Maybe a) #
Instance details Defined in Data.Strict.Classes Methods toStrict :: Maybe0 a -> Maybe a # toLazy :: Maybe a -> Maybe0 a #
type Rep (Maybe a) #
Instance details Defined in Data.Strict.Maybe type Rep (Maybe a) = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.4.0.1" '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 #
Instance details Defined in Data.Strict.Maybe type Rep1 Maybe = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.4.0.1" '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 #

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

isNothing :: Maybe a -> Bool #

Yields True iff the argument is Nothing.

fromJust :: Maybe a -> a #

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

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

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 #

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 #

Analogous to listToMaybe in Data.Maybe.

maybeToList :: Maybe a -> [a] #

Analogous to maybeToList in Data.Maybe.

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

Analogous to catMaybes in Data.Maybe.

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

Analogous to mapMaybe in Data.Maybe.