Data.Maybe.Strict

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.

Documentation

data Maybe a :: * -> *

The type of strict optional values.

Constructors

Nothing

Just ~a

Instances

Functor Maybe

Methods

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

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

Eq a => Eq (Maybe a)

Methods

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

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

Ord a => Ord (Maybe a)

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)

Methods

readsPrec :: Int -> ReadS (Maybe a)

readList :: ReadS [Maybe a]

readPrec :: ReadPrec (Maybe a)

readListPrec :: ReadPrec [Maybe a]

Show a => Show (Maybe a)

Methods

showsPrec :: Int -> Maybe a -> ShowS

show :: Maybe a -> String

showList :: [Maybe a] -> ShowS

type Rep (Maybe a)

type Rep (Maybe a) = D1 (MetaData "Maybe" "Data.Strict.Maybe" "strict-0.3.2-HHI2FPLqQto28EK1aExOvf" False) ((:+:) (C1 (MetaCons "Nothing" PrefixI False) U1) (C1 (MetaCons "Just" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness SourceLazy DecidedStrict) (Rec0 a))))

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.

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.

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.

_Just :: Prism (Maybe a) (Maybe b) a b

Analogous to _Just in Control.Lens.Prism

_Nothing :: Prism' (Maybe a) ()

Analogous to _Nothing in Control.Lens.Prism

Orphan instances

Foldable Maybe

Methods

fold :: Monoid m => Maybe m -> 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

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)

Data a => Data (Maybe a)

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)) -> Maybe (c (Maybe a))

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (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 :: (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)

Generic (Maybe a)

Associated Types

type Rep (Maybe a) :: * -> *

Methods

from :: Maybe a -> Rep (Maybe a) x

to :: Rep (Maybe a) x -> Maybe a

Monoid a => Monoid (Maybe a)

Methods

mempty :: Maybe a

mappend :: Maybe a -> Maybe a -> Maybe a

mconcat :: [Maybe a] -> Maybe a

Arbitrary a => Arbitrary (Maybe a)

Methods

arbitrary :: Gen (Maybe a)

shrink :: Maybe a -> [Maybe a]

Hashable a => Hashable (Maybe a)

Methods

hashWithSalt :: Int -> Maybe a -> Int

hash :: Maybe a -> Int

ToJSON a => ToJSON (Maybe a)

Methods

toJSON :: Maybe a -> Value

toEncoding :: Maybe a -> Encoding

toJSONList :: [Maybe a] -> Value

toEncodingList :: [Maybe a] -> Encoding

FromJSON a => FromJSON (Maybe a)

Methods

parseJSON :: Value -> Parser (Maybe a)

parseJSONList :: Value -> Parser [Maybe a]

Binary a => Binary (Maybe a)

Methods

put :: Maybe a -> Put

get :: Get (Maybe a)

putList :: [Maybe a] -> Put

NFData a => NFData (Maybe a)

Methods

rnf :: Maybe a -> ()

Strict (Maybe a) (Maybe a)

Methods

strict :: Iso' (Maybe a) (Maybe a)