Data.Strict.Maybe

strict-0.5.1: Strict data types and String IO.

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

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 -> () #
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) #
Hashable1 Maybe # |
Instance details Defined in Data.Strict.Maybe Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Maybe a -> Int #
Generic1 Maybe # |
Instance details Defined in Data.Strict.Maybe Associated Types
type Rep1 Maybe |
Instance details Defined in Data.Strict.Maybe type Rep1 Maybe = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.5.1-1mB1yRAtJfYEfaxRHR0qto" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) Par1))
Methods from1 :: Maybe a -> Rep1 Maybe a # to1 :: Rep1 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 -> () #
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 #
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 #
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)) -> 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 :: 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) #
Generic (Maybe a) # |
Instance details Defined in Data.Strict.Maybe Associated Types
type Rep (Maybe a) |
Instance details Defined in Data.Strict.Maybe type Rep (Maybe a) = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.5.1-1mB1yRAtJfYEfaxRHR0qto" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 a)))
Methods from :: Maybe a -> Rep (Maybe a) x # to :: Rep (Maybe a) x -> 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 #
Eq a => Eq (Maybe a) # |
Instance details Defined in Data.Strict.Maybe Methods (==) :: Maybe a -> Maybe a -> Bool # (/=) :: Maybe a -> Maybe a -> Bool #
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 #
Hashable a => Hashable (Maybe a) # |
Instance details Defined in Data.Strict.Maybe Methods hashWithSalt :: Int -> Maybe a -> Int # hash :: Maybe a -> Int #
Strict (Maybe a) (Maybe a) # |
Instance details Defined in Data.Strict.Classes Methods toStrict :: Maybe a -> Maybe a # toLazy :: Maybe a -> Maybe a #
type Rep1 Maybe # |
Instance details Defined in Data.Strict.Maybe type Rep1 Maybe = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.5.1-1mB1yRAtJfYEfaxRHR0qto" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) Par1))
type Rep (Maybe a) # |
Instance details Defined in Data.Strict.Maybe type Rep (Maybe a) = D1 ('MetaData "Maybe" "Data.Strict.Maybe" "strict-0.5.1-1mB1yRAtJfYEfaxRHR0qto" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 a)))

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.