Data.Either.Projections

Either Projections, inspired by Scala's Either.

Example:

>>> let process = (+) 100 . (4 *)
>>> let foo = fmap (10 *) . rightProjection

>>> let ok = Right 10 :: Either String Int
>>> let fail = Left "wrong input" :: Either String Int

>>> foo ok
RightProjection 140

>>> foo fail
RightNothing "wrong input"

>>> toMaybe $ foo fail
Nothing

>>> toMaybe $ foo ok
Just 140

>>> toEither $ foo fail
Left "wrong input"

>>> mergeEither . toEither . fmap show $ rightProjection ok
"10"

Projections.

class EitherProjection proj left right side | proj -> left, proj -> right, proj -> side where

A projection of Either.

Methods

toEither :: proj -> Either left right

toMaybe :: proj -> Maybe side

Instances

EitherProjection (RightProjection l r) l r r

EitherProjection (LeftProjection l r) l r l

type LeftProjection l r = LeftProjection' r l

Left projection.

data LeftProjection' r l

Left projection with type arguments flipped. | Allows to define instances of Functor, etc.

Instances

Functor (LeftProjection' r)

(Eq r, Eq l) => Eq (LeftProjection' r l)

(Ord r, Ord l) => Ord (LeftProjection' r l)

(Read r, Read l) => Read (LeftProjection' r l)

(Show r, Show l) => Show (LeftProjection' r l)

EitherProjection (LeftProjection l r) l r l

data RightProjection l r

Right projection.

Instances

Functor (RightProjection l)

(Eq l, Eq r) => Eq (RightProjection l r)

(Ord l, Ord r) => Ord (RightProjection l r)

(Read l, Read r) => Read (RightProjection l r)

(Show l, Show r) => Show (RightProjection l r)

EitherProjection (RightProjection l r) l r r

leftProjection :: Either l r -> LeftProjection l r

Get left projection.

rightProjection :: Either l r -> RightProjection l r

Get right projection.

misc

mergeEither :: Either a a -> a

Merge Left and Right. Inspired by Scala.