aivi.core.either

Either L R is a disjoint union with Left L and Right R branches. Use it when both branches are meaningful alternatives. For ordinary success and failure, prefer Result E A.

Type class operations

Either E implements Functor, Apply, Applicative, Chain, Monad, Foldable, and Traversable. Ambient map is equivalent to mapRight; pure constructs Right; chain and join short-circuit on Left. apply checks the function's Either first, preserving its Left when both inputs fail. reduce returns the seed for Left and visits the payload once for Right.

traverse transform either sequences the Right payload through any Applicative G, producing G (Either E B). A Left is lifted unchanged with pure; its payload is never passed to the transform. Traversing into Task builds a deferred plan.

Bifunctor Either supplies bimap, equivalent to mapBoth. Import this module's type or helpers to make its instances available.

API

Export	Type	Behavior
Either	Either L R	The two-branch type
Left	L -> Either L R	Construct the left branch
Right	R -> Either L R	Construct the right branch
isLeft	Either L R -> Bool	Test for Left
isRight	Either L R -> Bool	Test for Right
fromLeft	Either L R -> Option L	Extract a left value when present
fromRight	Either L R -> Option R	Extract a right value when present
mapLeft	(L1 -> L2) -> Either L1 R -> Either L2 R	Transform the left branch
mapRight	(R1 -> R2) -> Either L R1 -> Either L R2	Transform the right branch
mapBoth	(L1 -> L2) -> (R1 -> R2) -> Either L1 R1 -> Either L2 R2	Transform either branch
fold	(L -> C) -> (R -> C) -> Either L R -> C	Eliminate an Either into one result type
swap	Either L R -> Either R L	Exchange the branches
toOption	Either L R -> Option R	Keep Right; discard Left
toResult	Either L R -> Result L R	Map Left to Err and Right to Ok
fromResult	Result E A -> Either E A	Map Err to Left and Ok to Right
partitionEithers	List (Either L R) -> (List L, List R)	Split values into left and right lists while preserving order

use aivi.core.either (
    Either
    Left
    Right
    fold
)

type Either Text Int -> Text
func describe = value =>
    fold (message => "error: {message}") (number => "value: {number}") value

value example : Text = describe (Right 3)