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Add 'lookup' function to Data.Set #291

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2 changes: 2 additions & 0 deletions Data/Set.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,7 @@ module Data.Set (
, size
, member
, notMember
, lookup
, lookupLT
, lookupGT
, lookupLE
Expand Down Expand Up @@ -146,6 +147,7 @@ module Data.Set (
) where

import Data.Set.Base as S
import Prelude ()

-- $strictness
--
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18 changes: 17 additions & 1 deletion Data/Set/Base.hs
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Expand Up @@ -114,6 +114,7 @@ module Data.Set.Base (
, size
, member
, notMember
, lookup
, lookupLT
, lookupGT
, lookupLE
Expand Down Expand Up @@ -194,7 +195,7 @@ module Data.Set.Base (
, merge
) where

import Prelude hiding (filter,foldl,foldr,null,map)
import Prelude hiding (filter,foldl,foldr,null,map,lookup)
import qualified Data.List as List
import Data.Bits (shiftL, shiftR)
#if !MIN_VERSION_base(4,8,0)
Expand Down Expand Up @@ -370,6 +371,21 @@ notMember a t = not $ member a t
{-# INLINE notMember #-}
#endif

-- | /O(log n)/. Find the given element and return the copy contained in the set.
lookup :: Ord a => a -> Set a -> Maybe a
lookup = go
where
go !_ Tip = Nothing
go x (Bin _ y l r) = case compare x y of
LT -> go x l
GT -> go x r
EQ -> Just y
#if __GLASGOW_HASKELL__
{-# INLINABLE lookup #-}
#else
{-# INLINE lookup #-}
#endif

-- | /O(log n)/. Find largest element smaller than the given one.
--
-- > lookupLT 3 (fromList [3, 5]) == Nothing
Expand Down
12 changes: 11 additions & 1 deletion tests/set-properties.hs
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Expand Up @@ -12,7 +12,8 @@ import Test.HUnit hiding (Test, Testable)
import Test.QuickCheck

main :: IO ()
main = defaultMain [ testCase "lookupLT" test_lookupLT
main = defaultMain [ testCase "lookup" test_lookup
, testCase "lookupLT" test_lookupLT
, testCase "lookupGT" test_lookupGT
, testCase "lookupLE" test_lookupLE
, testCase "lookupGE" test_lookupGE
Expand All @@ -24,6 +25,7 @@ main = defaultMain [ testCase "lookupLT" test_lookupLT
, testProperty "prop_Single" prop_Single
, testProperty "prop_Member" prop_Member
, testProperty "prop_NotMember" prop_NotMember
, testProperty "prop_Lookup" prop_Lookup
, testProperty "prop_LookupLT" prop_LookupLT
, testProperty "prop_LookupGT" prop_LookupGT
, testProperty "prop_LookupLE" prop_LookupLE
Expand Down Expand Up @@ -73,6 +75,11 @@ main = defaultMain [ testCase "lookupLT" test_lookupLT
-- Unit tests
----------------------------------------------------------------

test_lookup :: Assertion
test_lookup = do
lookup 3 (fromList [3, 5]) @?= Just 3
lookup 4 (fromList [3, 5]) @?= Nothing

test_lookupLT :: Assertion
test_lookupLT = do
lookupLT 3 (fromList [3, 5]) @?= Nothing
Expand Down Expand Up @@ -192,6 +199,9 @@ test_LookupSomething lookup' cmp xs =
filter_odd [_] = []
filter_odd (_ : o : xs) = o : filter_odd xs

prop_Lookup :: [Int] -> Bool
prop_Lookup = test_LookupSomething lookup (==)

prop_LookupLT :: [Int] -> Bool
prop_LookupLT = test_LookupSomething lookupLT (<)

Expand Down