Data.These

The These type and associated operations.

Documentation

data These a b

The These type represents values with two non-exclusive possibilities.

This can be useful to represent combinations of two values, where the combination is defined if either input is. Algebraically, the type These A B represents (A + B + AB), which doesn't factor easily into sums and products--a type like Either A (B, Maybe A) is unclear and awkward to use.

These has straightforward instances of Functor, Monad, &c., and behaves like a hybrid error/writer monad, as would be expected.

Constructors

This a

That b

These a b

Instances

Bifoldable These

Defined in Data.These

Methods

bifold :: Monoid m => These m m -> m

bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> These a b -> m

bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> These a b -> c

bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> These a b -> c

Bifunctor These

Defined in Data.These

Methods

bimap :: (a -> b) -> (c -> d) -> These a c -> These b d

first :: (a -> b) -> These a c -> These b c

second :: (b -> c) -> These a b -> These a c

Bitraversable These

Defined in Data.These

Methods

bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> These a b -> f (These c d)

Foldable (These a)

Defined in Data.These

Methods

fold :: Monoid m => These a m -> m

foldMap :: Monoid m => (a0 -> m) -> These a a0 -> m

foldMap' :: Monoid m => (a0 -> m) -> These a a0 -> m

foldr :: (a0 -> b -> b) -> b -> These a a0 -> b

foldr' :: (a0 -> b -> b) -> b -> These a a0 -> b

foldl :: (b -> a0 -> b) -> b -> These a a0 -> b

foldl' :: (b -> a0 -> b) -> b -> These a a0 -> b

foldr1 :: (a0 -> a0 -> a0) -> These a a0 -> a0

foldl1 :: (a0 -> a0 -> a0) -> These a a0 -> a0

toList :: These a a0 -> [a0]

null :: These a a0 -> Bool

length :: These a a0 -> Int

elem :: Eq a0 => a0 -> These a a0 -> Bool

maximum :: Ord a0 => These a a0 -> a0

minimum :: Ord a0 => These a a0 -> a0

sum :: Num a0 => These a a0 -> a0

product :: Num a0 => These a a0 -> a0

Traversable (These a)

Defined in Data.These

Methods

traverse :: Applicative f => (a0 -> f b) -> These a a0 -> f (These a b)

sequenceA :: Applicative f => These a (f a0) -> f (These a a0)

mapM :: Monad m => (a0 -> m b) -> These a a0 -> m (These a b)

sequence :: Monad m => These a (m a0) -> m (These a a0)

Semigroup a => Applicative (These a)

Defined in Data.These

Methods

pure :: a0 -> These a a0

(<*>) :: These a (a0 -> b) -> These a a0 -> These a b

liftA2 :: (a0 -> b -> c) -> These a a0 -> These a b -> These a c

(*>) :: These a a0 -> These a b -> These a b

(<*) :: These a a0 -> These a b -> These a a0

Functor (These a)

Defined in Data.These

Methods

fmap :: (a0 -> b) -> These a a0 -> These a b

(<$) :: a0 -> These a b -> These a a0

Semigroup a => Monad (These a)

Defined in Data.These

Methods

(>>=) :: These a a0 -> (a0 -> These a b) -> These a b

(>>) :: These a a0 -> These a b -> These a b

return :: a0 -> These a a0

(Data a, Data b) => Data (These a b)

Defined in Data.These

Methods

gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> These a b -> c (These a b)

gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (These a b)

toConstr :: These a b -> Constr

dataTypeOf :: These a b -> DataType

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (These a b))

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

gmapT :: (forall b0. Data b0 => b0 -> b0) -> These a b -> These a b

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> These a b -> r

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> These a b -> r

gmapQ :: (forall d. Data d => d -> u) -> These a b -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> These a b -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> These a b -> m (These a b)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> These a b -> m (These a b)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> These a b -> m (These a b)

(Semigroup a, Semigroup b) => Semigroup (These a b)

Defined in Data.These

Methods

(<>) :: These a b -> These a b -> These a b

sconcat :: NonEmpty (These a b) -> These a b

stimes :: Integral b0 => b0 -> These a b -> These a b

Generic (These a b)

Defined in Data.These

Associated Types

type Rep (These a b) :: Type -> Type

Methods

from :: These a b -> Rep (These a b) x

to :: Rep (These a b) x -> These a b

(Read a, Read b) => Read (These a b)

Defined in Data.These

Methods

readsPrec :: Int -> ReadS (These a b)

readList :: ReadS [These a b]

readPrec :: ReadPrec (These a b)

readListPrec :: ReadPrec [These a b]

(Show a, Show b) => Show (These a b)

Defined in Data.These

Methods

showsPrec :: Int -> These a b -> ShowS

show :: These a b -> String

showList :: [These a b] -> ShowS

(NFData a, NFData b) => NFData (These a b)

Defined in Data.These

Methods

rnf :: These a b -> ()

(Eq a, Eq b) => Eq (These a b)

Defined in Data.These

Methods

(==) :: These a b -> These a b -> Bool

(/=) :: These a b -> These a b -> Bool

(Ord a, Ord b) => Ord (These a b)

Defined in Data.These

Methods

compare :: These a b -> These a b -> Ordering

(<) :: These a b -> These a b -> Bool

(<=) :: These a b -> These a b -> Bool

(>) :: These a b -> These a b -> Bool

(>=) :: These a b -> These a b -> Bool

max :: These a b -> These a b -> These a b

min :: These a b -> These a b -> These a b

type Rep (These a b)

Defined in Data.These

type Rep (These a b) = D1 ('MetaData "These" "Data.These" "these-skinny-0.7.6-CXhQEzyyAl4KEuzl0743fL" 'False) (C1 ('MetaCons "This" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)) :+: (C1 ('MetaCons "That" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 b)) :+: C1 ('MetaCons "These" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 b))))

Functions to get rid of These

these :: (a -> c) -> (b -> c) -> (a -> b -> c) -> These a b -> c

Case analysis for the These type.

fromThese :: a -> b -> These a b -> (a, b)

Takes two default values and produces a tuple.

mergeThese :: (a -> a -> a) -> These a a -> a

Coalesce with the provided operation.

mergeTheseWith :: (a -> c) -> (b -> c) -> (c -> c -> c) -> These a b -> c

BiMap and coalesce results with the provided operation.

Traversals

here :: Applicative f => (a -> f b) -> These a t -> f (These b t)

A Traversal of the first half of a These, suitable for use with Control.Lens.

there :: Applicative f => (a -> f b) -> These t a -> f (These t b)

A Traversal of the second half of a These, suitable for use with Control.Lens.

Case selections

justThis :: These a b -> Maybe a

justThis = preview _This

justThat :: These a b -> Maybe b

justThat = preview _That

justThese :: These a b -> Maybe (a, b)

justThese = preview _These

catThis :: [These a b] -> [a]

Select all This constructors from a list.

catThat :: [These a b] -> [b]

Select all That constructors from a list.

catThese :: [These a b] -> [(a, b)]

Select all These constructors from a list.

partitionThese :: [These a b] -> ([(a, b)], ([a], [b]))

Select each constructor and partition them into separate lists.

Case predicates

isThis :: These a b -> Bool

isThis = isJust . justThis

isThat :: These a b -> Bool

isThat = isJust . justThat

isThese :: These a b -> Bool

isThese = isJust . justThese

Map operations

mapThese :: (a -> c) -> (b -> d) -> These a b -> These c d

Bifunctor map.

mapThis :: (a -> c) -> These a b -> These c b

mapThis = over here

mapThat :: (b -> d) -> These a b -> These a d

mapThat = over there

For zipping and unzipping of structures with These values, see Data.Align.