Add set limit to range operation using submap (#75)

Author: tomcumming

CHANGELOG.md

@@ -7,6 +7,7 @@ Notable changes to this project are documented in this file. The format is based
 Breaking changes:
 
 New features:
+- Add `Data.Set.range` which works like `Data.Map.submap`.
 
 Bugfixes:
 

src/Data/Set.purs

@@ -18,6 +18,7 @@ module Data.Set
   , size
   , findMin
   , findMax
+  , range
   , union
   , unions
   , difference
@@ -136,6 +137,11 @@ findMin (Set m) = Prelude.map _.key (M.findMin m)
 findMax :: forall a. Set a -> Maybe a
 findMax (Set m) = Prelude.map _.key (M.findMax m)
 
+-- | Return the set limited to the lower and upper bounds (including keys equal
+-- | to those bounds).
+range :: forall a. Ord a => Maybe a -> Maybe a -> Set a -> Set a
+range kmin kmax (Set m) = Set (M.submap kmin kmax m)
+
 -- | Form the union of two sets
 -- |
 -- | Running time: `O(n + m)`

test/Test/Data/Set.purs

@@ -37,3 +37,8 @@ setTests = do
 
   log "toggle - deletes item"
   assert $ S.toggle 1 (S.fromFoldable [1]) == S.empty
+
+  log "range"
+  do let s1 = S.fromFoldable [1,2,3,4,5]
+         s2 = S.fromFoldable [2,3]
+     assert $ S.range (Just 2) (Just 3) s1 == s2