Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
This module exists to provide documentation for lenses for working with
Map
, which might otherwise be obscured by their genericity.
Map
is an instance of At
and provides at
as a lens on values at keys:
>>>
Map.fromList [(1, "world")] ^. at 1
Just "world"
>>>
Map.empty & at 1 .~ Just "world"
fromList [(1,"world")]
>>>
Map.empty & at 0 .~ Just "hello"
fromList [(0,"hello")]
We can traverse, fold over, and map over key-value pairs in a Map
,
thanks to indexed traversals, folds and setters.
>>>
iover imapped const $ Map.fromList [(1, "Venus")]
fromList [(1,1)]
>>>
ifoldMapOf ifolded (\i _ -> Sum i) $ Map.fromList [(2, "Earth"), (3, "Mars")]
Sum {getSum = 5}
>>>
itraverseOf_ ifolded (curry print) $ Map.fromList [(4, "Jupiter")]
(4,"Jupiter")
>>>
itoListOf ifolded $ Map.fromList [(5, "Saturn")]
[(5,"Saturn")]
A related class, Ixed
, allows us to use ix
to
traverse a value at a particular key.
>>>
Map.fromList [(2, "Earth")] & ix 2 %~ ("New " ++)
fromList [(2,"New Earth")]
>>>
preview (ix 8) Map.empty
Nothing
Synopsis
- toMapOf :: (Is k A_Fold, is `HasSingleIndex` i, Ord i) => Optic' k is s a -> s -> Map i a
- lt :: Ord k => k -> IxAffineTraversal' k (Map k v) v
- gt :: Ord k => k -> IxAffineTraversal' k (Map k v) v
- le :: Ord k => k -> IxAffineTraversal' k (Map k v) v
- ge :: Ord k => k -> IxAffineTraversal' k (Map k v) v
Documentation
toMapOf :: (Is k A_Fold, is `HasSingleIndex` i, Ord i) => Optic' k is s a -> s -> Map i a Source #
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) [('a',"alpha"),('b', "beta")]
fromList [('a',"alpha"),('b',"beta")]
>>>
toMapOf (ifolded <%> ifolded) ["foo", "bar"]
fromList [((0,0),'f'),((0,1),'o'),((0,2),'o'),((1,0),'b'),((1,1),'a'),((1,2),'r')]
>>>
toMapOf (folded % ifolded) [('a', "hello"), ('b', "world"), ('a', "dummy")]
fromList [('a',"hello"),('b',"world")]
lt :: Ord k => k -> IxAffineTraversal' k (Map k v) v Source #
Focus on the largest key smaller than the given one and its corresponding value.
>>>
Map.fromList [('a', "hi"), ('b', "there")] & over (lt 'b') (++ "!")
fromList [('a',"hi!"),('b',"there")]
>>>
ipreview (lt 'a') $ Map.fromList [('a', 'x'), ('b', 'y')]
Nothing
gt :: Ord k => k -> IxAffineTraversal' k (Map k v) v Source #
Focus on the smallest key greater than the given one and its corresponding value.
>>>
Map.fromList [('a', "hi"), ('b', "there")] & over (gt 'b') (++ "!")
fromList [('a',"hi"),('b',"there")]
>>>
ipreview (gt 'a') $ Map.fromList [('a', 'x'), ('b', 'y')]
Just ('b','y')
le :: Ord k => k -> IxAffineTraversal' k (Map k v) v Source #
Focus on the largest key smaller or equal than the given one and its corresponding value.
>>>
Map.fromList [('a', "hi"), ('b', "there")] & over (le 'b') (++ "!")
fromList [('a',"hi"),('b',"there!")]
>>>
ipreview (le 'a') $ Map.fromList [('a', 'x'), ('b', 'y')]
Just ('a','x')
ge :: Ord k => k -> IxAffineTraversal' k (Map k v) v Source #
Focus on the smallest key greater or equal than the given one and its corresponding value.
>>>
Map.fromList [('a', "hi"), ('c', "there")] & over (ge 'b') (++ "!")
fromList [('a',"hi"),('c',"there!")]
>>>
ipreview (ge 'b') $ Map.fromList [('a', 'x'), ('c', 'y')]
Just ('c','y')