Control.Lens.IndexedLens

Indexed Lenses

type IndexedLens i s t a b = forall f k. (Indexed i k, Functor f) => k (a -> f b) (s -> f t)

Every IndexedLens is a valid Lens and a valid IndexedTraversal.

Common Indexed Lenses

class At k m | m -> k where

Provides an IndexedLens that can be used to read, write or delete the value associated with a key in a map-like container.

Methods

at :: k -> SimpleIndexedLens k (m v) (Maybe v)

>>> Map.fromList [(1,"hello")] ^.at 1
Just "hello"

>>> at 1 ?~ "hello" $ Map.empty
fromList [(1,"hello")]

Instances

At Int IntMap

(Eq k, Hashable k) => At k (HashMap k)

Ord k => At k (Map k)

class Contains k m | m -> k where

Provides an IndexedLens that can be used to read, write or delete a member of a set-like container

Methods

contains :: k -> SimpleIndexedLens k m Bool

>>> contains 3 .~ False $ IntSet.fromList [1,2,3,4]
fromList [1,2,4]

Instances

Contains Int IntSet

(Eq k, Hashable k) => Contains k (HashSet k)

Ord k => Contains k (Set k)

resultAt :: Eq e => e -> SimpleIndexedLens e (e -> a) a

This lens can be used to change the result of a function but only where the arguments match the key given.

>>> let f = (+1) & resultAt 3 .~ 8 in (f 2, f 3)
(3,8)

Indexed Lens Combinators

(%%@~) :: Overloaded (Index i) f s t a b -> (i -> a -> f b) -> s -> f t

Adjust the target of an IndexedLens returning a supplementary result, or adjust all of the targets of an IndexedTraversal and return a monoidal summary of the supplementary results and the answer.

(%%@~) = withIndex

 (%%@~) :: Functor f => IndexedLens i s t a b      -> (i -> a -> f b) -> s -> f t
 (%%@~) :: Functor f => IndexedTraversal i s t a b -> (i -> a -> f b) -> s -> f t

In particular, it is often useful to think of this function as having one of these even more restrictive type signatures

 (%%@~) ::             IndexedLens i s t a b      -> (i -> a -> (r, b)) -> s -> (r, t)
 (%%@~) :: Monoid r => IndexedTraversal i s t a b -> (i -> a -> (r, b)) -> s -> (r, t)

(<%@~) :: Overloaded (Index i) ((,) b) s t a b -> (i -> a -> b) -> s -> (b, t)

Adjust the target of an IndexedLens returning the intermediate result, or adjust all of the targets of an IndexedTraversal and return a monoidal summary along with the answer.

l <%~ f = l <%@~ const f

When you do not need access to the index then (<%~) is more liberal in what it can accept.

If you do not need the intermediate result, you can use (%@~) or even (%~).

 (<%@~) ::             IndexedLens i s t a b -> (i -> a -> b) -> s -> (b, t)
 (<%@~) :: Monoid b => IndexedTraversal i s t a b -> (i -> a -> b) -> s -> (b, t)

(%%@=) :: MonadState s m => Overloaded (Index i) ((,) r) s s a b -> (i -> a -> (r, b)) -> m r

Adjust the target of an IndexedLens returning a supplementary result, or adjust all of the targets of an IndexedTraversal within the current state, and return a monoidal summary of the supplementary results.

l %%@= f = state (l %%@~ f)

 (%%@=) :: MonadState s m                IndexedLens i s s a b      -> (i -> a -> (r, b)) -> s -> m r
 (%%@=) :: (MonadState s m, Monoid r) => IndexedTraversal i s s a b -> (i -> a -> (r, b)) -> s -> m r

(<%@=) :: MonadState s m => Overloaded (Index i) ((,) b) s s a b -> (i -> a -> b) -> m b

Adjust the target of an IndexedLens returning the intermediate result, or adjust all of the targets of an IndexedTraversal within the current state, and return a monoidal summary of the intermediate results.

 (<%@=) :: MonadState s m                IndexedLens i s s a b      -> (i -> a -> b) -> m b
 (<%@=) :: (MonadState s m, Monoid b) => IndexedTraversal i s s a b -> (i -> a -> b) -> m b

Storing Indexed Lenses

newtype ReifiedIndexedLens i s t a b

Useful for storage.

Constructors

ReifyIndexedLens

Fields

reflectIndexedLens :: IndexedLens i s t a b

Simple

type SimpleIndexedLens i s a = IndexedLens i s s a a

type SimpleIndexedLens i = Simple (IndexedLens i)

type SimpleReifiedIndexedLens i s a = ReifiedIndexedLens i s s a a

type SimpleIndexedLens i = Simple (ReifiedIndexedLens i)