| Safe Haskell | Safe |
|---|---|
| Language | Haskell2010 |
Maybe
Synopsis
- data Maybe a
- maybe :: b -> (a -> b) -> Maybe a -> b
- maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b
- isJust :: Maybe a -> Bool
- isNothing :: Maybe a -> Bool
- fromMaybe :: a -> Maybe a -> a
- listToMaybe :: [a] -> Maybe a
- maybeToList :: Maybe a -> [a]
- catMaybes :: [Maybe a] -> [a]
- mapMaybe :: (a -> Maybe b) -> [a] -> [b]
- _Just :: (Choice p, Applicative f) => p a (f b) -> p (Maybe a) (f (Maybe b))
- _Nothing :: (Choice p, Applicative f) => p () (f ()) -> p (Maybe a) (f (Maybe a))
- newtype Option a = Option {}
- option :: b -> (a -> b) -> Option a -> b
- newtype First a = First {}
- newtype Last a = Last {}
Maybe
The Maybe type encapsulates an optional value. A value of type
Maybe aa (represented as Just aNothing). 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.
Instances
| Monad Maybe | Since: base-2.1 |
| Functor Maybe | Since: base-2.1 |
| MonadFix Maybe | Since: base-2.1 |
Defined in Control.Monad.Fix | |
| MonadFail Maybe | Since: base-4.9.0.0 |
Defined in Control.Monad.Fail | |
| Applicative Maybe | Since: base-2.1 |
| 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 # 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 # elem :: Eq a => a -> Maybe a -> Bool # maximum :: Ord a => Maybe a -> a # minimum :: Ord a => Maybe a -> a # | |
| Traversable Maybe | Since: base-2.1 |
| Alternative Maybe | Since: base-2.1 |
| ToJSON1 Maybe | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Maybe a -> Value # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Maybe a] -> Value # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Maybe a -> Encoding # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Maybe a] -> Encoding # | |
| FromJSON1 Maybe | |
| MonadPlus Maybe | Since: base-2.1 |
| Eq1 Maybe | Since: base-4.9.0.0 |
| Ord1 Maybe | Since: base-4.9.0.0 |
Defined in Data.Functor.Classes | |
| Read1 Maybe | Since: base-4.9.0.0 |
Defined in Data.Functor.Classes | |
| Show1 Maybe | Since: base-4.9.0.0 |
| MonadZip Maybe | Since: base-4.8.0.0 |
| Compactable Maybe | |
Defined in Control.Compactable Methods compact :: Maybe (Maybe a) -> Maybe a # separate :: Maybe (Either l r) -> (Maybe l, Maybe r) # filter :: (a -> Bool) -> Maybe a -> Maybe a # partition :: (a -> Bool) -> Maybe a -> (Maybe a, Maybe a) # fmapMaybe :: Functor Maybe => (a -> Maybe b) -> Maybe a -> Maybe b # fmapEither :: Functor Maybe => (a -> Either l r) -> Maybe a -> (Maybe l, Maybe r) # applyMaybe :: Applicative Maybe => Maybe (a -> Maybe b) -> Maybe a -> Maybe b # applyEither :: Applicative Maybe => Maybe (a -> Either l r) -> Maybe a -> (Maybe l, Maybe r) # bindMaybe :: Monad Maybe => Maybe a -> (a -> Maybe (Maybe b)) -> Maybe b # bindEither :: Monad Maybe => Maybe a -> (a -> Maybe (Either l r)) -> (Maybe l, Maybe r) # traverseMaybe :: (Applicative g, Traversable Maybe) => (a -> g (Maybe b)) -> Maybe a -> g (Maybe b) # traverseEither :: (Applicative g, Traversable Maybe) => (a -> g (Either l r)) -> Maybe a -> g (Maybe l, Maybe r) # | |
| CompactFold Maybe | |
Defined in Control.Compactable Methods compactFold :: Foldable g => Maybe (g a) -> Maybe a # separateFold :: Bifoldable g => Maybe (g a b) -> (Maybe a, Maybe b) # fmapFold :: (Functor Maybe, Foldable g) => (a -> g b) -> Maybe a -> Maybe b # fmapBifold :: (Functor Maybe, Bifoldable g) => (a -> g l r) -> Maybe a -> (Maybe l, Maybe r) # applyFold :: (Applicative Maybe, Foldable g) => Maybe (a -> g b) -> Maybe a -> Maybe b # applyBifold :: (Applicative Maybe, Bifoldable g) => Maybe (a -> g l r) -> Maybe a -> (Maybe l, Maybe r) # bindFold :: (Monad Maybe, Foldable g) => Maybe a -> (a -> Maybe (g b)) -> Maybe b # bindBifold :: (Monad Maybe, Bifoldable g) => Maybe a -> (a -> Maybe (g l r)) -> (Maybe l, Maybe r) # traverseFold :: (Applicative h, Foldable g, Traversable Maybe) => (a -> h (g b)) -> Maybe a -> h (Maybe b) # traverseBifold :: (Applicative h, Bifoldable g, Traversable Maybe) => (a -> h (g l r)) -> Maybe a -> h (Maybe l, Maybe r) # | |
| NFData1 Maybe | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| MonadThrow Maybe | |
Defined in Control.Monad.Catch | |
| Hashable1 Maybe | |
Defined in Data.Hashable.Class | |
| Apply Maybe | |
| Pointed Maybe | |
Defined in Data.Pointed | |
| Plus Maybe | |
Defined in Data.Functor.Plus | |
| Alt Maybe | |
| Bind Maybe | |
| Extend Maybe | |
| MonadError () Maybe | Since: mtl-2.2.2 |
Defined in Control.Monad.Error.Class | |
| MonadBase Maybe Maybe | |
Defined in Control.Monad.Base | |
| (Selector s, GToJSON enc arity (K1 i (Maybe a) :: * -> *), KeyValuePair enc pairs, Monoid pairs) => RecordToPairs enc pairs arity (S1 s (K1 i (Maybe a) :: * -> *)) | |
Defined in Data.Aeson.Types.ToJSON | |
| () :=> (Functor Maybe) | |
| () :=> (Applicative Maybe) | |
Defined in Data.Constraint Methods ins :: () :- Applicative Maybe # | |
| () :=> (Alternative Maybe) | |
Defined in Data.Constraint Methods ins :: () :- Alternative Maybe # | |
| () :=> (MonadPlus Maybe) | |
| (Selector s, FromJSON a) => FromRecord arity (S1 s (K1 i (Maybe a) :: * -> *)) | |
Defined in Data.Aeson.Types.FromJSON | |
| Eq a => Eq (Maybe a) | |
| Data a => Data (Maybe a) | Since: base-4.0.0.0 |
Defined in Data.Data 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) # | |
| Ord a => Ord (Maybe a) | |
| Read a => Read (Maybe a) | Since: base-2.1 |
| Show a => Show (Maybe a) | |
| Generic (Maybe a) | |
| Semigroup a => Semigroup (Maybe a) | Since: base-4.9.0.0 |
| Semigroup a => Monoid (Maybe a) | Lift a semigroup into Since 4.11.0: constraint on inner Since: base-2.1 |
| Lift a => Lift (Maybe a) | |
| Hashable a => Hashable (Maybe a) | |
Defined in Data.Hashable.Class | |
| ToJSON a => ToJSON (Maybe a) | |
Defined in Data.Aeson.Types.ToJSON | |
| FromJSON a => FromJSON (Maybe a) | |
| SingKind a => SingKind (Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
| NFData a => NFData (Maybe a) | |
Defined in Control.DeepSeq | |
| Ixed (Maybe a) | |
Defined in Control.Lens.At | |
| At (Maybe a) | |
| AsEmpty (Maybe a) | |
Defined in Control.Lens.Empty | |
| Pretty a => Pretty (Maybe a) | Ignore
|
Defined in Data.Text.Prettyprint.Doc.Internal | |
| Lower (Maybe a) | |
Defined in Data.Semilattice.Lower Methods lowerBound :: Maybe a # | |
| Serialise a => Serialise (Maybe a) | Since: serialise-0.2.0.0 |
| Generic1 Maybe | |
| SingI (Nothing :: Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
| (Eq a) :=> (Eq (Maybe a)) | |
| (Ord a) :=> (Ord (Maybe a)) | |
| (Read a) :=> (Read (Maybe a)) | |
| (Show a) :=> (Show (Maybe a)) | |
| (Semigroup a) :=> (Semigroup (Maybe a)) | |
| (Monoid a) :=> (Monoid (Maybe a)) | |
| Each (Maybe a) (Maybe b) a b |
|
| SingI a2 => SingI (Just a2 :: Maybe a1) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
| (Selector c, ToJSON a) => GtoJson (M1 S c (K1 i (Maybe a) :: * -> *)) | |
| (Selector c, FromJSON a) => GfromJson (M1 S c (K1 i (Maybe a) :: * -> *)) | |
| type Rep (Maybe a) | |
| data Sing (b :: Maybe a) | |
| type DemoteRep (Maybe a) | |
Defined in GHC.Generics | |
| type Index (Maybe a) | |
Defined in Control.Lens.At | |
| type IxValue (Maybe a) | |
Defined in Control.Lens.At | |
| type Rep1 Maybe | |
maybe :: b -> (a -> b) -> Maybe a -> b #
The maybe function takes a default value, a function, and a Maybe
value. If the Maybe value is Nothing, the function returns the
default value. Otherwise, it applies the function to the value inside
the Just and returns the result.
Examples
Basic usage:
>>>maybe False odd (Just 3)True
>>>maybe False odd NothingFalse
Read an integer from a string using readMaybe. If we succeed,
return twice the integer; that is, apply (*2) to it. If instead
we fail to parse an integer, return 0 by default:
>>>import Text.Read ( readMaybe )>>>maybe 0 (*2) (readMaybe "5")10>>>maybe 0 (*2) (readMaybe "")0
Apply show to a Maybe Int. If we have Just n, we want to show
the underlying Int n. But if we have Nothing, we return the
empty string instead of (for example) "Nothing":
>>>maybe "" show (Just 5)"5">>>maybe "" show Nothing""
fromMaybe :: a -> Maybe a -> a #
The fromMaybe function takes a default value and and Maybe
value. If the Maybe is Nothing, it returns the default values;
otherwise, it returns the value contained in the Maybe.
Examples
Basic usage:
>>>fromMaybe "" (Just "Hello, World!")"Hello, World!"
>>>fromMaybe "" Nothing""
Read an integer from a string using readMaybe. If we fail to
parse an integer, we want to return 0 by default:
>>>import Text.Read ( readMaybe )>>>fromMaybe 0 (readMaybe "5")5>>>fromMaybe 0 (readMaybe "")0
listToMaybe :: [a] -> Maybe a #
The listToMaybe function returns Nothing on an empty list
or Just aa is the first element of the list.
Examples
Basic usage:
>>>listToMaybe []Nothing
>>>listToMaybe [9]Just 9
>>>listToMaybe [1,2,3]Just 1
Composing maybeToList with listToMaybe should be the identity
on singleton/empty lists:
>>>maybeToList $ listToMaybe [5][5]>>>maybeToList $ listToMaybe [][]
But not on lists with more than one element:
>>>maybeToList $ listToMaybe [1,2,3][1]
maybeToList :: Maybe a -> [a] #
The maybeToList function returns an empty list when given
Nothing or a singleton list when not given Nothing.
Examples
Basic usage:
>>>maybeToList (Just 7)[7]
>>>maybeToList Nothing[]
One can use maybeToList to avoid pattern matching when combined
with a function that (safely) works on lists:
>>>import Text.Read ( readMaybe )>>>sum $ maybeToList (readMaybe "3")3>>>sum $ maybeToList (readMaybe "")0
catMaybes :: [Maybe a] -> [a] #
The catMaybes function takes a list of Maybes and returns
a list of all the Just values.
Examples
Basic usage:
>>>catMaybes [Just 1, Nothing, Just 3][1,3]
When constructing a list of Maybe values, catMaybes can be used
to return all of the "success" results (if the list is the result
of a map, then mapMaybe would be more appropriate):
>>>import Text.Read ( readMaybe )>>>[readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ][Just 1,Nothing,Just 3]>>>catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ][1,3]
mapMaybe :: (a -> Maybe b) -> [a] -> [b] #
The mapMaybe function is a version of map which can throw
out elements. In particular, the functional argument returns
something of type Maybe bNothing, no element
is added on to the result list. If it is Just bb is
included in the result list.
Examples
Using mapMaybe f xcatMaybes $ map f x
>>>import Text.Read ( readMaybe )>>>let readMaybeInt = readMaybe :: String -> Maybe Int>>>mapMaybe readMaybeInt ["1", "Foo", "3"][1,3]>>>catMaybes $ map readMaybeInt ["1", "Foo", "3"][1,3]
If we map the Just constructor, the entire list should be returned:
>>>mapMaybe Just [1,2,3][1,2,3]
Prisms
_Just :: (Choice p, Applicative f) => p a (f b) -> p (Maybe a) (f (Maybe b)) #
This Prism provides a Traversal for tweaking the target of the value of Just in a Maybe.
>>>over _Just (+1) (Just 2)Just 3
Unlike traverse this is a Prism, and so you can use it to inject as well:
>>>_Just # 5Just 5
>>>5^.re _JustJust 5
Interestingly,
m^?_Just≡ m
>>>Just x ^? _JustJust x
>>>Nothing ^? _JustNothing
Newtypes
Option is effectively Maybe with a better instance of
Monoid, built off of an underlying Semigroup instead of an
underlying Monoid.
Ideally, this type would not exist at all and we would just fix the
Monoid instance of Maybe
Instances
| Monad Option | Since: base-4.9.0.0 |
| Functor Option | Since: base-4.9.0.0 |
| MonadFix Option | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Applicative Option | Since: base-4.9.0.0 |
| Foldable Option | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => Option m -> m # foldMap :: Monoid m => (a -> m) -> Option a -> m # foldr :: (a -> b -> b) -> b -> Option a -> b # foldr' :: (a -> b -> b) -> b -> Option a -> b # foldl :: (b -> a -> b) -> b -> Option a -> b # foldl' :: (b -> a -> b) -> b -> Option a -> b # foldr1 :: (a -> a -> a) -> Option a -> a # foldl1 :: (a -> a -> a) -> Option a -> a # elem :: Eq a => a -> Option a -> Bool # maximum :: Ord a => Option a -> a # minimum :: Ord a => Option a -> a # | |
| Traversable Option | Since: base-4.9.0.0 |
| Alternative Option | Since: base-4.9.0.0 |
| ToJSON1 Option | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Option a -> Value # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Option a] -> Value # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Option a -> Encoding # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Option a] -> Encoding # | |
| FromJSON1 Option | |
| MonadPlus Option | Since: base-4.9.0.0 |
| Compactable Option | |
Defined in Control.Compactable Methods compact :: Option (Maybe a) -> Option a # separate :: Option (Either l r) -> (Option l, Option r) # filter :: (a -> Bool) -> Option a -> Option a # partition :: (a -> Bool) -> Option a -> (Option a, Option a) # fmapMaybe :: Functor Option => (a -> Maybe b) -> Option a -> Option b # fmapEither :: Functor Option => (a -> Either l r) -> Option a -> (Option l, Option r) # applyMaybe :: Applicative Option => Option (a -> Maybe b) -> Option a -> Option b # applyEither :: Applicative Option => Option (a -> Either l r) -> Option a -> (Option l, Option r) # bindMaybe :: Monad Option => Option a -> (a -> Option (Maybe b)) -> Option b # bindEither :: Monad Option => Option a -> (a -> Option (Either l r)) -> (Option l, Option r) # traverseMaybe :: (Applicative g, Traversable Option) => (a -> g (Maybe b)) -> Option a -> g (Option b) # traverseEither :: (Applicative g, Traversable Option) => (a -> g (Either l r)) -> Option a -> g (Option l, Option r) # | |
| CompactFold Option | |
Defined in Control.Compactable Methods compactFold :: Foldable g => Option (g a) -> Option a # separateFold :: Bifoldable g => Option (g a b) -> (Option a, Option b) # fmapFold :: (Functor Option, Foldable g) => (a -> g b) -> Option a -> Option b # fmapBifold :: (Functor Option, Bifoldable g) => (a -> g l r) -> Option a -> (Option l, Option r) # applyFold :: (Applicative Option, Foldable g) => Option (a -> g b) -> Option a -> Option b # applyBifold :: (Applicative Option, Bifoldable g) => Option (a -> g l r) -> Option a -> (Option l, Option r) # bindFold :: (Monad Option, Foldable g) => Option a -> (a -> Option (g b)) -> Option b # bindBifold :: (Monad Option, Bifoldable g) => Option a -> (a -> Option (g l r)) -> (Option l, Option r) # traverseFold :: (Applicative h, Foldable g, Traversable Option) => (a -> h (g b)) -> Option a -> h (Option b) # traverseBifold :: (Applicative h, Bifoldable g, Traversable Option) => (a -> h (g l r)) -> Option a -> h (Option l, Option r) # | |
| NFData1 Option | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Apply Option | |
| Pointed Option | |
Defined in Data.Pointed | |
| Plus Option | |
Defined in Data.Functor.Plus | |
| Alt Option | |
| Bind Option | |
| (Selector s, GToJSON enc arity (K1 i (Maybe a) :: * -> *), KeyValuePair enc pairs, Monoid pairs) => RecordToPairs enc pairs arity (S1 s (K1 i (Option a) :: * -> *)) | |
Defined in Data.Aeson.Types.ToJSON | |
| (Selector s, FromJSON a) => FromRecord arity (S1 s (K1 i (Option a) :: * -> *)) | |
Defined in Data.Aeson.Types.FromJSON | |
| Eq a => Eq (Option a) | |
| Data a => Data (Option a) | |
Defined in Data.Semigroup Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Option a -> c (Option a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Option a) # toConstr :: Option a -> Constr # dataTypeOf :: Option a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Option a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Option a)) # gmapT :: (forall b. Data b => b -> b) -> Option a -> Option a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Option a -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Option a -> r # gmapQ :: (forall d. Data d => d -> u) -> Option a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Option a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Option a -> m (Option a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Option a -> m (Option a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Option a -> m (Option a) # | |
| Ord a => Ord (Option a) | |
Defined in Data.Semigroup | |
| Read a => Read (Option a) | |
| Show a => Show (Option a) | |
| Generic (Option a) | |
| Semigroup a => Semigroup (Option a) | Since: base-4.9.0.0 |
| Semigroup a => Monoid (Option a) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Option a) | |
Defined in Data.Hashable.Class | |
| ToJSON a => ToJSON (Option a) | |
Defined in Data.Aeson.Types.ToJSON | |
| FromJSON a => FromJSON (Option a) | |
| NFData a => NFData (Option a) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Wrapped (Option a) | |
| Serialise a => Serialise (Option a) | Since: serialise-0.2.0.0 |
| Generic1 Option | |
| t ~ Option b => Rewrapped (Option a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep (Option a) | |
Defined in Data.Semigroup | |
| type Unwrapped (Option a) | |
Defined in Control.Lens.Wrapped | |
| type Rep1 Option | |
Defined in Data.Semigroup | |
Maybe monoid returning the leftmost non-Nothing value.
First aAlt Maybe a
>>>getFirst (First (Just "hello") <> First Nothing <> First (Just "world"))Just "hello"
Instances
| Monad First | |
| Functor First | |
| MonadFix First | Since: base-4.8.0.0 |
Defined in Control.Monad.Fix | |
| Applicative First | |
| Foldable First | Since: base-4.8.0.0 |
Defined in Data.Foldable Methods fold :: Monoid m => First m -> m # foldMap :: Monoid m => (a -> m) -> First a -> m # foldr :: (a -> b -> b) -> b -> First a -> b # foldr' :: (a -> b -> b) -> b -> First a -> b # foldl :: (b -> a -> b) -> b -> First a -> b # foldl' :: (b -> a -> b) -> b -> First a -> b # foldr1 :: (a -> a -> a) -> First a -> a # foldl1 :: (a -> a -> a) -> First a -> a # elem :: Eq a => a -> First a -> Bool # maximum :: Ord a => First a -> a # minimum :: Ord a => First a -> a # | |
| Traversable First | Since: base-4.8.0.0 |
| ToJSON1 First | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> First a -> Value # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [First a] -> Value # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> First a -> Encoding # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [First a] -> Encoding # | |
| FromJSON1 First | |
| MonadZip First | Since: base-4.8.0.0 |
| NFData1 First | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Apply First | |
| Pointed First | |
Defined in Data.Pointed | |
| Plus First | |
Defined in Data.Functor.Plus | |
| Alt First | |
| Bind First | |
| Eq a => Eq (First a) | |
| Data a => Data (First a) | Since: base-4.8.0.0 |
Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> First a -> c (First a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (First a) # toConstr :: First a -> Constr # dataTypeOf :: First a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (First a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (First a)) # gmapT :: (forall b. Data b => b -> b) -> First a -> First a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> First a -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> First a -> r # gmapQ :: (forall d. Data d => d -> u) -> First a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> First a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> First a -> m (First a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> First a -> m (First a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> First a -> m (First a) # | |
| Ord a => Ord (First a) | |
| Read a => Read (First a) | |
| Show a => Show (First a) | |
| Generic (First a) | |
| Semigroup (First a) | Since: base-4.9.0.0 |
| Monoid (First a) | Since: base-2.1 |
| ToJSON a => ToJSON (First a) | |
Defined in Data.Aeson.Types.ToJSON | |
| FromJSON a => FromJSON (First a) | |
| NFData a => NFData (First a) | Since: deepseq-1.4.0.0 |
Defined in Control.DeepSeq | |
| Wrapped (First a) | |
| AsEmpty (First a) | |
Defined in Control.Lens.Empty | |
| Lower (First a) | |
Defined in Data.Semilattice.Lower Methods lowerBound :: First a # | |
| Serialise a => Serialise (First a) | Since: serialise-0.2.0.0 |
| Generic1 First | |
| t ~ First b => Rewrapped (First a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep (First a) | |
Defined in Data.Monoid | |
| type Unwrapped (First a) | |
Defined in Control.Lens.Wrapped | |
| type Rep1 First | |
Defined in Data.Monoid | |
Maybe monoid returning the rightmost non-Nothing value.
Last aDual (First a)Dual (Alt Maybe a)
>>>getLast (Last (Just "hello") <> Last Nothing <> Last (Just "world"))Just "world"
Instances
| Monad Last | |
| Functor Last | |
| MonadFix Last | Since: base-4.8.0.0 |
Defined in Control.Monad.Fix | |
| Applicative Last | |
| Foldable Last | Since: base-4.8.0.0 |
Defined in Data.Foldable Methods fold :: Monoid m => Last m -> m # foldMap :: Monoid m => (a -> m) -> Last a -> m # foldr :: (a -> b -> b) -> b -> Last a -> b # foldr' :: (a -> b -> b) -> b -> Last a -> b # foldl :: (b -> a -> b) -> b -> Last a -> b # foldl' :: (b -> a -> b) -> b -> Last a -> b # foldr1 :: (a -> a -> a) -> Last a -> a # foldl1 :: (a -> a -> a) -> Last a -> a # elem :: Eq a => a -> Last a -> Bool # maximum :: Ord a => Last a -> a # | |
| Traversable Last | Since: base-4.8.0.0 |
| ToJSON1 Last | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Last a -> Value # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Last a] -> Value # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Last a -> Encoding # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Last a] -> Encoding # | |
| FromJSON1 Last | |
| MonadZip Last | Since: base-4.8.0.0 |
| NFData1 Last | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Apply Last | |
| Pointed Last | |
Defined in Data.Pointed | |
| Plus Last | |
Defined in Data.Functor.Plus | |
| Alt Last | |
| Bind Last | |
| Eq a => Eq (Last a) | |
| Data a => Data (Last a) | Since: base-4.8.0.0 |
Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Last a -> c (Last a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Last a) # toConstr :: Last a -> Constr # dataTypeOf :: Last a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Last a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Last a)) # gmapT :: (forall b. Data b => b -> b) -> Last a -> Last a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Last a -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Last a -> r # gmapQ :: (forall d. Data d => d -> u) -> Last a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Last a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # | |
| Ord a => Ord (Last a) | |
| Read a => Read (Last a) | |
| Show a => Show (Last a) | |
| Generic (Last a) | |
| Semigroup (Last a) | Since: base-4.9.0.0 |
| Monoid (Last a) | Since: base-2.1 |
| ToJSON a => ToJSON (Last a) | |
Defined in Data.Aeson.Types.ToJSON | |
| FromJSON a => FromJSON (Last a) | |
| NFData a => NFData (Last a) | Since: deepseq-1.4.0.0 |
Defined in Control.DeepSeq | |
| Wrapped (Last a) | |
| AsEmpty (Last a) | |
Defined in Control.Lens.Empty | |
| Lower (Last a) | |
Defined in Data.Semilattice.Lower Methods lowerBound :: Last a # | |
| Serialise a => Serialise (Last a) | Since: serialise-0.2.0.0 |
| Generic1 Last | |
| t ~ Last b => Rewrapped (Last a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep (Last a) | |
Defined in Data.Monoid | |
| type Unwrapped (Last a) | |
Defined in Control.Lens.Wrapped | |
| type Rep1 Last | |
Defined in Data.Monoid | |