indexed-traversable

FunctorWithIndex, FoldableWithIndex, TraversableWithIndex

Version on this page:0.1.2
LTS Haskell 23.24:0.1.4@rev:1
Stackage Nightly 2025-05-27:0.1.4@rev:1
Latest on Hackage:0.1.4@rev:1

See all snapshots indexed-traversable appears in

BSD-2-Clause licensed by Edward Kmett
Maintained by Oleg Grenrus
This version can be pinned in stack with:indexed-traversable-0.1.2@sha256:8e8e39c730741495bd597716a74560f996b189520ec2a58b08a29de2dc5ea872,2497

Module documentation for 0.1.2

This package provides three useful generalizations:

class Functor f => FunctorWithIndex i f | f -> i where
  imap :: (i -> a -> b) -> f a -> f b

class Foldable f => FoldableWithIndex i f | f -> i where
  ifoldMap :: Monoid m => (i -> a -> m) -> f a -> m

class (FunctorWithIndex i t, FoldableWithIndex i t, Traversable t) => TraversableWithIndex i t | t -> i where
  itraverse :: Applicative f => (i -> a -> f b) -> t a -> f (t b)

This package contains instances for types in GHC boot libraries. For some additional instances see indexed-traversable-instances.

The keys package provides similar functionality, but uses (associated) TypeFamilies instead of FunctionalDependencies.

Changes

0.1.2 [2021-10-30]

  • Changed (<$>) + (<*>) to liftA2 to potentially avoid extra fmap.
  • Add (#..), coercive composition after a 2-parameter function.
  • Switched references to lens ‘Of’- functions to base functions.

Thanks to wygulmage for contributions.

0.1.1 [2020-12-27]

0.1 [2020-12-15]

  • Split out and combine this package functionality from lens and optics