| Portability | non-portable |
|---|---|
| Stability | experimental |
| Maintainer | Edward Kmett <ekmett@gmail.com> |
| Safe Haskell | Trustworthy |
Control.Lens.At
Description
At
class Ixed m => At m whereSource
At provides a Lens that can be used to read,
write or delete the value associated with a key in a Map-like
container on an ad hoc basis.
An instance of At should satisfy:
ixk ≡atk.traverse
Methods
Ixed
This simple AffineTraversal lets you traverse the value at a given
key in a Map or element at an ordinal position in a list or Seq.
Methods
ix :: Index m -> Traversal' m (IxValue m)Source
This simple AffineTraversal lets you traverse the value at a given
key in a Map or element at an ordinal position in a list or Seq.
NB: Setting the value of this AffineTraversal will only set the value in the
Lens if it is already present.
If you want to be able to insert missing values, you want at.
>>>Seq.fromList [a,b,c,d] & ix 2 %~ ffromList [a,b,f c,d]
>>>Seq.fromList [a,b,c,d] & ix 2 .~ efromList [a,b,e,d]
>>>Seq.fromList [a,b,c,d] ^? ix 2Just c
>>>Seq.fromList [] ^? ix 2Nothing
Instances
| Ixed ByteString | |
| Ixed ByteString | |
| Ixed Text | |
| Ixed Value | |
| Ixed IntSet | |
| Ixed Text | |
| Ixed [a] | |
| Ixed (Maybe a) | |
| Ixed (Identity a) | |
| Ixed (Tree a) | |
| Ixed (Seq a) | |
| Ixed (IntMap a) | |
| Ord k => Ixed (Set k) | |
| Ixed (NonEmpty a) | |
| (Eq k, Hashable k) => Ixed (HashSet k) | |
| Ixed (Vector a) | |
| Unbox a => Ixed (Vector a) | |
| Storable a => Ixed (Vector a) | |
| Prim a => Ixed (Vector a) | |
| ~ * a b => Ixed (a, b) | |
| (Eq k, Hashable k) => Ixed (HashMap k a) | |
| Ord k => Ixed (Map k a) | |
| (IArray UArray e, Ix i) => Ixed (UArray i e) | arr |
| Ix i => Ixed (Array i e) | arr |
| (~ * a b, ~ * a c) => Ixed (a, b, c) | |
| (~ * a b, ~ * a c, ~ * a d) => Ixed (a, b, c, d) | |
| (~ * a b, ~ * a c, ~ * a d, ~ * a e) => Ixed (a, b, c, d, e) | |
| (~ * a b, ~ * a c, ~ * a d, ~ * a e, ~ * a f) => Ixed (a, b, c, d, e, f) | |
| (~ * a b, ~ * a c, ~ * a d, ~ * a e, ~ * a f, ~ * a g) => Ixed (a, b, c, d, e, f, g) | |
| (~ * a b, ~ * a c, ~ * a d, ~ * a e, ~ * a f, ~ * a g, ~ * a h) => Ixed (a, b, c, d, e, f, g, h) | |
| (~ * a b, ~ * a c, ~ * a d, ~ * a e, ~ * a f, ~ * a g, ~ * a h, ~ * a i) => Ixed (a, b, c, d, e, f, g, h, i) |
Contains
This class provides a simple IndexedFold (or IndexedTraversal) that lets you view (and modify)
information about whether or not a container contains a given Index.