Safe Haskell	None
Language	Haskell2010

Data.IntMap.Optics

Description

IntMap is an instance of At and provides at as a lens on values at keys:

>>> IntMap.fromList [(1, "world")] ^. at 1
Just "world"

>>> IntMap.empty & at 1 .~ Just "world"
fromList [(1,"world")]

>>> IntMap.empty & at 0 .~ Just "hello"
fromList [(0,"hello")]

We can traverse, fold over, and map over key-value pairs in an IntMap, thanks to indexed traversals, folds and setters.

>>> iover imapped const $ IntMap.fromList [(1, "Venus")]
fromList [(1,1)]

>>> ifoldMapOf ifolded (\i _ -> Sum i) $ IntMap.fromList [(2, "Earth"), (3, "Mars")]
Sum {getSum = 5}

>>> itraverseOf_ ifolded (curry print) $ IntMap.fromList [(4, "Jupiter")]
(4,"Jupiter")

>>> itoListOf ifolded $ IntMap.fromList [(5, "Saturn")]
[(5,"Saturn")]

A related class, Ixed, allows us to use ix to traverse a value at a particular key.

>>> IntMap.fromList [(2, "Earth")] & ix 2 %~ ("New " ++)
fromList [(2,"New Earth")]

>>> preview (ix 8) IntMap.empty
Nothing

Synopsis

Documentation

Construct a map from an IxFold.

The construction is left-biased (see union), i.e. the first occurrences of keys in the fold or traversal order are preferred.

>>> toMapOf ifolded ["hello", "world"]
fromList [(0,"hello"),(1,"world")]

>>> toMapOf (folded % ifolded) [(1,"alpha"),(2, "beta")]
fromList [(1,"alpha"),(2,"beta")]

>>> toMapOf (icompose (\a b -> 10*a+b) $ ifolded % ifolded) ["foo", "bar"]
fromList [(0,'f'),(1,'o'),(2,'o'),(10,'b'),(11,'a'),(12,'r')]

>>> toMapOf (folded % ifolded) [(1, "hello"), (2, "world"), (1, "dummy")]
fromList [(1,"hello"),(2,"world")]

Focus on the largest key smaller than the given one and its corresponding value.

>>> IntMap.fromList [(1, "hi"), (2, "there")] & over (lt 2) (++ "!")
fromList [(1,"hi!"),(2,"there")]

>>> ipreview (lt 1) $ IntMap.fromList [(1, 'x'), (2, 'y')]
Nothing

Focus on the smallest key greater than the given one and its corresponding value.

>>> IntMap.fromList [(1, "hi"), (2, "there")] & over (gt 2) (++ "!")
fromList [(1,"hi"),(2,"there")]

>>> ipreview (gt 1) $ IntMap.fromList [(1, 'x'), (2, 'y')]
Just (2,'y')

Focus on the largest key smaller or equal than the given one and its corresponding value.

>>> IntMap.fromList [(1, "hi"), (2, "there")] & over (le 2) (++ "!")
fromList [(1,"hi"),(2,"there!")]

>>> ipreview (le 1) $ IntMap.fromList [(1, 'x'), (2, 'y')]
Just (1,'x')

Focus on the smallest key greater or equal than the given one and its corresponding value.

>>> IntMap.fromList [(1, "hi"), (3, "there")] & over (ge 2) (++ "!")
fromList [(1,"hi"),(3,"there!")]

>>> ipreview (ge 2) $ IntMap.fromList [(1, 'x'), (3, 'y')]
Just (3,'y')