Data.Maybe.Linear

This module provides linear functions on the standard Maybe type.

Documentation

data Maybe a

The Maybe type encapsulates an optional value. A value of type Maybe a either contains a value of type a (represented as Just a), or it is empty (represented as Nothing). Using Maybe is a good way to deal with errors or exceptional cases without resorting to drastic measures such as error.

The Maybe type is also a monad. It is a simple kind of error monad, where all errors are represented by Nothing. A richer error monad can be built using the Either type.

Constructors

Nothing

Just a

Instances

MonadFail Maybe

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> Maybe a

Foldable Maybe

Since: base-2.1

Defined in Data.Foldable

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

Eq1 Maybe

Since: base-4.9.0.0

Defined in Data.Functor.Classes

Methods

liftEq :: (a -> b -> Bool) -> Maybe a -> Maybe b -> Bool

Ord1 Maybe

Since: base-4.9.0.0

Defined in Data.Functor.Classes

Methods

liftCompare :: (a -> b -> Ordering) -> Maybe a -> Maybe b -> Ordering

Read1 Maybe

Since: base-4.9.0.0

Defined in Data.Functor.Classes

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

Since: base-4.9.0.0

Defined in Data.Functor.Classes

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Maybe a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Maybe a] -> ShowS

Traversable Maybe

Since: base-2.1

Defined in Data.Traversable

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)

Alternative Maybe

Since: base-2.1

Defined in GHC.Base

Methods

empty :: Maybe a

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

some :: Maybe a -> Maybe [a]

many :: Maybe a -> Maybe [a]

Applicative Maybe

Since: base-2.1

Defined in GHC.Base

Methods

pure :: a -> Maybe a

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

liftA2 :: (a -> b -> c) -> Maybe a -> Maybe b -> Maybe c

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

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

Functor Maybe

Since: base-2.1

Defined in GHC.Base

Methods

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

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

Monad Maybe

Since: base-2.1

Defined in GHC.Base

Methods

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

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

return :: a -> Maybe a

MonadPlus Maybe

Since: base-2.1

Defined in GHC.Base

Methods

mzero :: Maybe a

mplus :: Maybe a -> Maybe a -> Maybe a

Hashable1 Maybe

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Maybe a -> Int

Functor Maybe

Defined in Data.Functor.Linear.Internal.Functor

Methods

fmap :: (a %1 -> b) -> Maybe a %1 -> Maybe b

Traversable Maybe

Defined in Data.Functor.Linear.Internal.Traversable

Methods

traverse :: Applicative f => (a %1 -> f b) -> Maybe a %1 -> f (Maybe b)

sequence :: Applicative f => Maybe (f a) %1 -> f (Maybe a)

Generic1 Maybe

Defined in GHC.Generics

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

Lift a => Lift (Maybe a :: Type)

Defined in Language.Haskell.TH.Syntax

Methods

lift :: Quote m => Maybe a -> m Exp

liftTyped :: forall (m :: Type -> Type). Quote m => Maybe a -> Code m (Maybe a)

Storable a => Storable (Maybe a)

Defined in Foreign.Marshal.Pure.Internal

Methods

sizeOf :: Maybe a -> Int

alignment :: Maybe a -> Int

peekElemOff :: Ptr (Maybe a) -> Int -> IO (Maybe a)

pokeElemOff :: Ptr (Maybe a) -> Int -> Maybe a -> IO ()

peekByteOff :: Ptr b -> Int -> IO (Maybe a)

pokeByteOff :: Ptr b -> Int -> Maybe a -> IO ()

peek :: Ptr (Maybe a) -> IO (Maybe a)

poke :: Ptr (Maybe a) -> Maybe a -> IO ()

Semigroup a => Monoid (Maybe a)

Lift a semigroup into Maybe forming a Monoid according to http://en.wikipedia.org/wiki/Monoid: "Any semigroup S may be turned into a monoid simply by adjoining an element e not in S and defining e*e = e and e*s = s = s*e for all s ∈ S."

Since 4.11.0: constraint on inner a value generalised from Monoid to Semigroup.

Since: base-2.1

Defined in GHC.Base

Methods

mempty :: Maybe a

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

mconcat :: [Maybe a] -> Maybe a

Semigroup a => Semigroup (Maybe a)

Since: base-4.9.0.0

Defined in GHC.Base

Methods

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

sconcat :: NonEmpty (Maybe a) -> Maybe a

stimes :: Integral b => b -> Maybe a -> Maybe a

Generic (Maybe a)

Defined in GHC.Generics

Associated Types

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

Methods

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

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

SingKind a => SingKind (Maybe a)

Since: base-4.9.0.0

Defined in GHC.Generics

Associated Types

type DemoteRep (Maybe a)

Methods

fromSing :: forall (a0 :: Maybe a). Sing a0 -> DemoteRep (Maybe a)

Read a => Read (Maybe a)

Since: base-2.1

Defined in GHC.Read

Methods

readsPrec :: Int -> ReadS (Maybe a)

readList :: ReadS [Maybe a]

readPrec :: ReadPrec (Maybe a)

readListPrec :: ReadPrec [Maybe a]

Show a => Show (Maybe a)

Since: base-2.1

Defined in GHC.Show

Methods

showsPrec :: Int -> Maybe a -> ShowS

show :: Maybe a -> String

showList :: [Maybe a] -> ShowS

Eq a => Eq (Maybe a)

Since: base-2.1

Defined in GHC.Maybe

Methods

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

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

Ord a => Ord (Maybe a)

Since: base-2.1

Defined in GHC.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)

Defined in Data.Hashable.Class

Methods

hashWithSalt :: Int -> Maybe a -> Int

hash :: Maybe a -> Int

Semigroup a => Monoid (Maybe a)

Defined in Data.Monoid.Linear.Internal.Monoid

Methods

mempty :: Maybe a

Semigroup a => Semigroup (Maybe a)

Defined in Data.Monoid.Linear.Internal.Semigroup

Methods

(<>) :: Maybe a %1 -> Maybe a %1 -> Maybe a

(Consumable a, Eq a) => Eq (Maybe a)

Defined in Data.Ord.Linear.Internal.Eq

Methods

(==) :: Maybe a %1 -> Maybe a %1 -> Bool

(/=) :: Maybe a %1 -> Maybe a %1 -> Bool

(Consumable a, Ord a) => Ord (Maybe a)

Defined in Data.Ord.Linear.Internal.Ord

Methods

compare :: Maybe a %1 -> Maybe a %1 -> Ordering

(<=) :: Maybe a %1 -> Maybe a %1 -> Bool

(<) :: Maybe a %1 -> Maybe a %1 -> Bool

(>) :: Maybe a %1 -> Maybe a %1 -> Bool

(>=) :: Maybe a %1 -> Maybe a %1 -> Bool

Consumable a => Consumable (Maybe a)

Defined in Data.Unrestricted.Linear.Internal.Consumable

Methods

consume :: Maybe a %1 -> ()

Dupable a => Dupable (Maybe a)

Defined in Data.Unrestricted.Linear.Internal.Dupable

Methods

dupR :: Maybe a %1 -> Replicator (Maybe a)

dup2 :: Maybe a %1 -> (Maybe a, Maybe a)

Movable a => Movable (Maybe a)

Defined in Data.Unrestricted.Linear.Internal.Movable

Methods

move :: Maybe a %1 -> Ur (Maybe a)

KnownRepresentable a => KnownRepresentable (Maybe a)

Defined in Foreign.Marshal.Pure.Internal

Methods

storable :: Dict (Storable (Maybe a))

Representable a => Representable (Maybe a)

Defined in Foreign.Marshal.Pure.Internal

Associated Types

type AsKnown (Maybe a)

Methods

toKnown :: Maybe a %1 -> AsKnown (Maybe a)

ofKnown :: AsKnown (Maybe a) %1 -> Maybe a

SingI ('Nothing :: Maybe a)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

sing :: Sing 'Nothing

SingI a2 => SingI ('Just a2 :: Maybe a1)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

sing :: Sing ('Just a2)

type Rep1 Maybe

Since: base-4.6.0.0

Defined in GHC.Generics

type Rep1 Maybe = D1 ('MetaData "Maybe" "GHC.Maybe" "base" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))

type Rep1 Maybe

Defined in Generics.Linear.Instances.Base

type Rep1 Maybe = D1 ('MetaData "Maybe" "GHC.Maybe" "base" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))

type DemoteRep (Maybe a)

Defined in GHC.Generics

type DemoteRep (Maybe a) = Maybe (DemoteRep a)

type Rep (Maybe a)

Since: base-4.6.0.0

Defined in GHC.Generics

type Rep (Maybe a) = D1 ('MetaData "Maybe" "GHC.Maybe" "base" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))

data Sing (b :: Maybe a)

Defined in GHC.Generics

data Sing (b :: Maybe a) where

• SNothing :: forall {a}. Sing ('Nothing :: Maybe a)
• SJust :: forall {a} (a1 :: a). Sing a1 -> Sing ('Just a1)

type AsKnown (Maybe a)

Defined in Foreign.Marshal.Pure.Internal

type AsKnown (Maybe a) = Maybe (AsKnown a)

type Rep (Maybe a)

Defined in Generics.Linear.Instances.Base

type Rep (Maybe a) = D1 ('MetaData "Maybe" "GHC.Maybe" "base" 'False) (C1 ('MetaCons "Nothing" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Just" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))

maybe :: b -> (a %1 -> b) -> Maybe a %1 -> b

maybe b f m returns (f a) where a is in m if it exists and b otherwise

fromMaybe :: a -> Maybe a %1 -> a

fromMaybe default m is the a in m if it exists and the default otherwise

maybeToList :: Maybe a %1 -> [a]

maybeToList m creates a singleton or an empty list based on the Maybe a.

catMaybes :: [Maybe a] %1 -> [a]

catMaybes xs discards the Nothings in xs and extracts the as

mapMaybe :: (a %1 -> Maybe b) -> [a] %1 -> [b]

mapMaybe f xs = catMaybes (map f xs)