either

An either monad transformer

Version on this page:	4.4.1
LTS Haskell 20.24:	5.0.2@rev:1
Stackage Nightly 2023-06-04:	5.0.2@rev:1
Latest on Hackage:	5.0.2@rev:1

See all snapshots either appears in

BSD-3-Clause licensed by Edward A. Kmett

Maintained by Edward A. Kmett

This version can be pinned in stack with:either-4.4.1@sha256:85a6e87bb53f52b2bfb6ef4be7a4e6e1abcb703726f09c1c2a1c7e95d6f95982,1468

Module documentation for 4.4.1

Control
- Control.Monad
  - Control.Monad.Trans
    - Control.Monad.Trans.Either
Data
- Data.Either
  - Data.Either.Combinators
  - Data.Either.Validation

Depends on 13 packages(full list with versions):

base, bifunctors, exceptions, free, mmorph, monad-control, MonadRandom, mtl, profunctors, semigroupoids, semigroups, transformers, transformers-base

Used by 21 packages in lts-3.22(full list with versions):

either

This provides an Either monad transformer that unlike ErrorT is unencumbered by a constraint on its Left hand argument. This is needed for a number of applications of this monad transformer, notably in recursion-schemes.

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.

-Edward Kmett

Changes

4.4

Support mmorph

4.3.4.1

Support MonadRandom 0.4

4.3.4

Support bifunctors 5, profunctors 5, and semigroupoids 5.

4.3.3.3

Fixed and enhanced documentation for eitherToError.

4.3.3.2

Support exceptions 0.8

4.3.3.1

Support exceptions 0.7

4.3.3

Added eitherToError.

4.3.2.1

Support monad-control 1.0

4.3.2

Added Validation.

4.3.0.2

Updated MonadRandom support.

4.3.0.1

Fixed import of MonadCatch to support versions of base before 4.6

4.3

Inverted dependency between free and either.

4.2

Added instances for MonadThrow, MonadCatch.

4.1

Added instances for MonadBase, MonadBaseControl, and MonadTransControl.

4.0

Updated dependencies.

3.4.2

Added ‘Data.Either.Combinators’.

3.4.1

Trustworthy despite UndecidableInstances

3.4

Delegate fail to the underlying Monad, rather than error.

3.3

Inverted roles between Semigroup and Alt. This let us write Alternative and MonadPlus instances that are compatible.
Removed the Functor constraint on most instances in exchange for incurring a Monad constraint on Traversable. EitherT is after all, a Monad transformer first and foremost.

3.2

Changed the Semigroup to use a Semigroup to combine Left branches. Left Alt untouched, so you can mix and match.

3.1

Added instances for mtl classes and MonadRandom.
The meaning of mapEitherT has changed to match mapErrorT in the mtl. The old mapEitherT is now bimapEitherT.

3.0.3

Started CHANGELOG