index package:lens

This allows you to filter an IndexedFold, IndexedGetter, IndexedTraversal or IndexedLens based on an index.

>>> ["hello","the","world","!!!"]^?traversed.index 2
Just "world"

Build a function from an indexed function.

Transform a Traversal into an IndexedTraversal or a Fold into an IndexedFold, etc.

indexing :: Traversal s t a b -> IndexedTraversal Int s t a b
indexing :: Prism s t a b     -> IndexedTraversal Int s t a b
indexing :: Lens s t a b      -> IndexedLens Int  s t a b
indexing :: Iso s t a b       -> IndexedLens Int s t a b
indexing :: Fold s a          -> IndexedFold Int s a
indexing :: Getter s a        -> IndexedGetter Int s a

indexing :: Indexable Int p => LensLike (Indexing f) s t a b -> Over p f s t a b

Transform a Traversal into an IndexedTraversal or a Fold into an IndexedFold, etc. This combinator is like indexing except that it handles large traversals and folds gracefully.

indexing64 :: Traversal s t a b -> IndexedTraversal Int64 s t a b
indexing64 :: Prism s t a b     -> IndexedTraversal Int64 s t a b
indexing64 :: Lens s t a b      -> IndexedLens Int64 s t a b
indexing64 :: Iso s t a b       -> IndexedLens Int64 s t a b
indexing64 :: Fold s a          -> IndexedFold Int64 s a
indexing64 :: Getter s a        -> IndexedGetter Int64 s a

indexing64 :: Indexable Int64 p => LensLike (Indexing64 f) s t a b -> Over p f s t a b

An IndexPreservingFold can be used as a Fold, but when composed with an IndexedTraversal, IndexedFold, or IndexedLens yields an IndexedFold respectively.

An IndexPreservingGetter can be used as a Getter, but when composed with an IndexedTraversal, IndexedFold, or IndexedLens yields an IndexedFold, IndexedFold or IndexedGetter respectively.

An IndexPreservingLens leaves any index it is composed with alone.

type IndexPreservingLens' = Simple IndexPreservingLens

An IndexPreservingSetter can be composed with a IndexedSetter, IndexedTraversal or IndexedLens and leaves the index intact, yielding an IndexedSetter.

type IndexedPreservingSetter' i = Simple IndexedPreservingSetter

An IndexPreservingTraversal leaves any index it is composed with alone.

type IndexPreservingTraversal' = Simple IndexPreservingTraversal

This class permits overloading of function application for things that also admit a notion of a key or index.

A function with access to a index. This constructor may be useful when you need to store an Indexable in a container to avoid ImpredicativeTypes.

index :: Indexed i a b -> i -> a -> b

Every IndexedFold is a valid Fold and can be used for Getting.

Every IndexedGetter is a valid IndexedFold and can be used for Getting like a Getter.