Control.Lens.IndexedTraversal

Indexed Traversals

type IndexedTraversal i a b c d = forall f k. (Indexed i k, Applicative f) => k (c -> f d) (a -> f b)

Every indexed traversal is a valid Traversal or IndexedFold.

The Indexed constraint is used to allow an IndexedTraversal to be used directly as a Traversal.

The Traversal laws are still required to hold.

Common Indexed Traversals

traverseAt :: At k m => k -> SimpleIndexedTraversal k (m v) v

Traverse the value at a given key in a map

traverseAt k = at k <. traverse

iwhereOf :: (Indexed i k, Applicative f) => Overloaded (Index i) f a b c c -> (i -> Bool) -> Overloaded k f a b c c

Access the element of an IndexedTraversal where the index matches a predicate.

>>> :m + Control.Lens
>>> over (iwhereOf (indexed traverse) (>0)) reverse $ ["He","was","stressed","o_O"]
["He","saw","desserts","O_o"]

 iwhereOf :: IndexedFold i a b            -> (i -> Bool) -> IndexedFold i a b
 iwhereOf :: IndexedGetter i a b          -> (i -> Bool) -> IndexedFold i a b
 iwhereOf :: SimpleIndexedLens i a b      -> (i -> Bool) -> SimpleIndexedTraversal i a b
 iwhereOf :: SimpleIndexedTraversal i a b -> (i -> Bool) -> SimpleIndexedTraversal i a b
 iwhereOf :: SimpleIndexedSetter i a b    -> (i -> Bool) -> SimpleIndexedSetter i a b

value :: (k -> Bool) -> SimpleIndexedTraversal k (k, v) v

This provides a Traversal that checks a predicate on a key before allowing you to traverse into a value.

Indexed Traversal Combinators

itraverseOf :: Overloaded (Index i) f a b c d -> (i -> c -> f d) -> a -> f b

Traversal with an index.

NB: When you don't need access to the index then you can just apply your IndexedTraversal directly as a function!

 itraverseOf = withIndex
 traverseOf l = itraverseOf l . const = id

 itraverseOf :: IndexedLens i a b c d      -> (i -> c -> f d) -> a -> f b
 itraverseOf :: IndexedTraversal i a b c d -> (i -> c -> f d) -> a -> f b

iforOf :: Overloaded (Index i) f a b c d -> a -> (i -> c -> f d) -> f b

Traverse with an index (and the arguments flipped)

forOf l a = iforOf l a . const

iforOf = flip . itraverseOf

 iforOf :: IndexedLens i a b c d      -> a -> (i -> c -> f d) -> f b
 iforOf :: IndexedTraversal i a b c d -> a -> (i -> c -> f d) -> f b

imapMOf :: Overloaded (Index i) (WrappedMonad m) a b c d -> (i -> c -> m d) -> a -> m b

Map each element of a structure targeted by a lens to a monadic action, evaluate these actions from left to right, and collect the results, with access its position.

When you don't need access to the index mapMOf is more liberal in what it can accept.

mapMOf l = imapMOf l . const

 imapMOf :: Monad m => IndexedLens      i a b c d -> (i -> c -> m d) -> a -> m b
 imapMOf :: Monad m => IndexedTraversal i a b c d -> (i -> c -> m d) -> a -> m b

iforMOf :: Overloaded (Index i) (WrappedMonad m) a b c d -> a -> (i -> c -> m d) -> m b

Map each element of a structure targeted by a lens to a monadic action, evaluate these actions from left to right, and collect the results, with access its position (and the arguments flipped).

 forMOf l a = iforMOf l a . const
 iforMOf = flip . imapMOf

 iforMOf :: Monad m => IndexedLens i a b c d      -> a -> (i -> c -> m d) -> m b
 iforMOf :: Monad m => IndexedTraversal i a b c d -> a -> (i -> c -> m d) -> m b

imapAccumROf :: Overloaded (Index i) (State s) a b c d -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)

Generalizes mapAccumR to an arbitrary IndexedTraversal with access to the index.

imapAccumROf accumulates state from right to left.

mapAccumROf l = imapAccumROf l . const

 imapAccumROf :: IndexedLens i a b c d      -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)
 imapAccumROf :: IndexedTraversal i a b c d -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)

imapAccumLOf :: Overloaded (Index i) (Backwards (State s)) a b c d -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)

Generalizes mapAccumL to an arbitrary IndexedTraversal with access to the index.

imapAccumLOf accumulates state from left to right.

mapAccumLOf l = imapAccumLOf l . const

 imapAccumLOf :: IndexedLens i a b c d      -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)
 imapAccumLOf :: IndexedTraversal i a b c d -> (i -> s -> c -> (s, d)) -> s -> a -> (s, b)

Storing Indexed Traversals

newtype ReifiedIndexedTraversal i a b c d

Useful for storage.

Constructors

ReifyIndexedTraversal

Fields

reflectIndexedTraversal :: IndexedTraversal i a b c d

Simple

type SimpleIndexedTraversal i a b = IndexedTraversal i a a b b

type SimpleIndexedTraversal i = Simple (IndexedTraversal i)

type SimpleReifiedIndexedTraversal i a b = ReifiedIndexedTraversal i a a b b

type SimpleIndexedTraversal i = Simple (ReifiedIndexedTraversal i)