Either

Lean: Hale.Base.Either | Haskell: Data.Either

Overview

Sum type with Left and Right constructors. Right-biased for Functor/Monad instances. Includes partitioning of lists of Either values.

API Mapping

Lean	Haskell	Kind
`Either`	`Either`	Type
`left` / `right`	`Left` / `Right`	Constructors
`isLeft` / `isRight`	`isLeft` / `isRight`	Predicate
`fromLeft` / `fromRight`	`fromLeft` / `fromRight`	Accessor
`either`	`either`	Eliminator
`mapLeft` / `mapRight`	`first` / `second`	Function
`swap`	N/A	Function
`partitionEithers`	`partitionEithers`	Function

Instances

Functor (Either a)
Pure (Either a)
Bind (Either a)
Seq (Either a)
Applicative (Either a)
Monad (Either a)
Bifunctor Either
ToString (Either a b) (requires ToString a, ToString b)

Proofs & Guarantees

swap_swap — swap (swap e) = e (involution)
isLeft_not_isRight — isLeft e = !isRight e
partitionEithers_length — total elements preserved after partitioning

Example

-- Partition a list of Either values
Either.partitionEithers [.left "a", .right 1, .left "b", .right 2]
-- => (["a", "b"], [1, 2])