these-0.4.1: An either-or-both data type, with corresponding hybrid error/writer monad transformer.

Safe Haskell	Safe-Inferred

Data.These

Contents

Functions to get rid of These
Traversals
Prisms
Case selections
Case predicates
Map operations

Description

The These type and associated operations. Now enhanced with Control.Lens magic!

Synopsis

Documentation

data These a b Source

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

Bitraversable1 These
Bitraversable These
Bifunctor These
Bifoldable1 These
Bifoldable These
Bicrosswalk These
Monoid c => MonadChronicle c (These c)
Monoid a => Monad (These a)
Functor (These a)
Monoid a => Applicative (These a)
Foldable (These a)
Traversable (These a)
Monoid a => Apply (These a)
Monoid a => Bind (These a)
Crosswalk (These a)
(Eq a, Eq b) => Eq (These a b)
(Ord a, Ord b) => Ord (These a b)
(Read a, Read b) => Read (These a b)
(Show a, Show b) => Show (These a b)
(Semigroup a, Semigroup b) => Semigroup (These a b)

Functions to get rid of `These`

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

Case analysis for the These type.

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

Takes two default values and produces a tuple.

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

Coalesce with the provided operation.

Traversals

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

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)Source

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

Prisms

_This :: (Choice p, Applicative f) => p a (f a) -> p (These a b) (f (These a b))Source

A Prism selecting the This constructor.

_That :: (Choice p, Applicative f) => p b (f b) -> p (These a b) (f (These a b))Source

A Prism selecting the That constructor.

_These :: (Choice p, Applicative f) => p (a, b) (f (a, b)) -> p (These a b) (f (These a b))Source

A Prism selecting the These constructor. These names are ridiculous!

Case selections

justThis :: These a b -> Maybe aSource

justThis = preview _This

justThat :: These a b -> Maybe bSource

justThat = preview _That

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

justThese = preview _These

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

Select all This constructors from a list.

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

Select all That constructors from a list.

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

Select all These constructors from a list.

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

Select each constructor and partition them into separate lists.

Case predicates

isThis :: These a b -> Bool Source

isThis = isJust . justThis

isThat :: These a b -> Bool Source

isThat = isJust . justThat

isThese :: These a b -> Bool Source

isThese = isJust . justThese

Map operations

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

Bifunctor map.

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

mapThis = over here

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

mapThat = over there

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