these

An either-or-both data type.

https://github.com/isomorphism/these

Version on this page:1.1.1.1
LTS Haskell 23.25:1.2.1@rev:2
Stackage Nightly 2025-06-18:1.2.1@rev:2
Latest on Hackage:1.2.1@rev:2

See all snapshots these appears in

BSD-3-Clause licensed by C. McCann, Oleg Grenrus
Maintained by Oleg Grenrus
This version can be pinned in stack with:these-1.1.1.1@sha256:3b63a3942f1da4ff97786221e3c654b969b54d570fef2cf4db97da4ea26a36cc,2609

Module documentation for 1.1.1.1

This package provides a data type These a b which can hold a value of either type or values of each type. This is usually thought of as an "inclusive or" type (contrasting Either a b as "exclusive or") or as an "outer join" type (contrasting (a, b) as "inner join").

data These a b = This a | That b | These a b

Since version 1, this package was split into parts:

Changes

1.1.1.1

  • Workaround GCC-4 C-preprocessor bug

1.1.1

  • These doesn’t depend on base-compat anymore
  • Add NFData1/2, Hashable1/2, Eq1/2 … instances

1.1

  • Reverse dependency with aeson.
    • The QuickCheck instances are moved into quickcheck-instances
    • The semigroupoids instances are gone for now.

1.0.1

  • add partitionEithersNE :: NonEmpty (Either a b) -> These (NonEmpty a) (NonEmpty b)

1

This is major package reogranisation. Old these were split into

  • these providing only These type and some combinators
  • these-lens providing lens combinators
  • semialign providing Semialign, Align, Zip, Unalign and Unzip classes
  • semialign-indexed providing SemialignWithIndex (izipWith and ialignWith members).
  • monad-chronicle providing ChronicleT and MonadChronicle

Also noticeable change is unalign :: f (These a b) -> (f a, f b). For the old f (These a b) -> (f (Maybe a), f (Maybe b)) use unzipWith (unalign . Just).

  • Many instances are added.
  • Since annotations are removed for all but these package.

0.8.1

  • Add Semialign Tree, Tagged, (->) e; Align Compose and Proxy instances
  • Allow semigroups-0.19 and hashable-1.3

0.8.0

  • Split align and alignWith into own class: Semialign.
  • ialign has default implementation
  • Add Semialign NonEmpty and Identity instances
  • Add Swap and Assoc instances (type classes from assoc package)
  • Move optics into Data.These.Lens module, and and some combinators Data.These.Combinators. Also some combinators are renamed, so naming is now consistent. As the result Data.These has very minimal exports.
  • Change type of partitionThese (nested pairs to triple)
  • Add partitionHereThere :: [These a b] -> ([a],[b])

0.7.6

  • Tigthen lower bounds
  • Add dependency on lens
  • Add assoc, reassoc, swap and Swapped instance
  • Add since annotations for things added in 0.7.x
  • Add AlignWithKey ZipList instance
  • Add Data.Align.Indexed module.
  • Add Data.Functor.These with These1 data type.
  • Add associativity law
  • Add toList property to enforce “align”-feel.
  • Map and IntMap Align instances implemented using merge combinators (when available)

0.7.5

  • Add Compose and (,) Crosswalk instances
  • Add bitraverseThese
  • GHC-8.6 support

0.7.4

  • QuickCheck-2.10 support: Arbitrary1/2 instances
  • GHC-8.2 support

0.7.3

  • Add salign :: (Align f, Semigroup a) => f a -> f a -> f a

0.7.2

  • Support aeson-1: add FromJSON1, FromJSON2 ToJSON1, and ToJSON2 These instances.

0.7.1

  • Add AlignWithKey in Data.Align.Key (added dependency keys)
  • Add These instances for
    • binary: Binary
    • aeson: FromJSON, ToJSON
    • QuickCheck: Arbitrary, CoArbitrary, Function
    • deepseq: NFData

0.7

  • Breaking change: Generalized Monad, Applicative instances of These and Chronicle to require only a Semigroup constraint
  • More efficient Align Seq implementation
  • Add Crosswalk Seq and Vector instances

0.6.2.1

  • Support quickcheck-instances-0.3.12 (tests)

0.6.2.0

  • Add support to bifunctors-5.1