lens-1.9.1: Lenses, Folds and Traversals

MaintainerEdward Kmett <ekmett@gmail.com>
Safe HaskellSafe-Infered






contains :: Int -> Simple Lens IntSet BoolSource

This Lens can be used to read, write or delete a member of an IntSet

 ghci> contains 3 +~ False $ fromList [1,2,3,4]
 fromList [1,2,4]
contains :: Functor f => Int -> (Bool -> f Bool) -> IntSet -> f IntSet

members :: Fold IntSet IntSource

IntSet isn't Foldable, but this Fold can be used to access the members of an IntSet.

>>> sumOf members $ setOf folded [1,2,3,4]

setmapped :: Simple Setter IntSet IntSource

This Setter can be used to change the contents of an IntSet by mapping the elements to new values.

Sadly, you can't create a valid Traversal for a Set, because the number of elements might change but you can manipulate it by reading using folded and reindexing it via setmap.

>>> adjust setmapped (+1) (fromList [1,2,3,4])
fromList [2,3,4,5]

setOf :: Getting IntSet a Int -> a -> IntSetSource

Construct an IntSet from a Getter, Fold, Traversal, Lens or Iso.

>>> :m + Data.IntSet.Lens Control.Lens
>>> setOf (folded._2) [("hello",1),("world",2),("!!!",3)]
fromList [1,2,3]
 setOf :: Getter a Int           -> a -> IntSet
 setOf :: Fold a Int             -> a -> IntSet
 setOf :: Simple Iso a Int       -> a -> IntSet
 setOf :: Simple Lens a Int      -> a -> IntSet
 setOf :: Simple Traversal a Int -> a -> IntSet