# lookup +containers

O(min(n,W)). Lookup the value at a key in the map. See also lookup.
O(log n). Lookup the value at a key in the map. The function will return the corresponding value as (Just value), or Nothing if the key isn't in the map. An example of using lookup: > import Prelude hiding (lookup) > import Data.Map > > employeeDept = fromList([("John","Sales"), ("Bob","IT")]) > deptCountry = fromList([("IT","USA"), ("Sales","France")]) > countryCurrency = fromList([("USA", "Dollar"), ("France", "Euro")]) > > employeeCurrency :: String -> Maybe String > employeeCurrency name = do > dept <- lookup name employeeDept > country <- lookup dept deptCountry > lookup country countryCurrency > > main = do > putStrLn \$ "John's currency: " ++ (show (employeeCurrency "John")) > putStrLn \$ "Pete's currency: " ++ (show (employeeCurrency "Pete")) The output of this program: > John's currency: Just "Euro" > Pete's currency: Nothing
O(log n). Find smallest element greater or equal to the given one. > lookupGE 3 (fromList [3, 5]) == Just 3 > lookupGE 4 (fromList [3, 5]) == Just 5 > lookupGE 6 (fromList [3, 5]) == Nothing
O(log n). Find smallest key greater or equal to the given one and return the corresponding (key, value) pair. > lookupGE 3 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a') > lookupGE 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b') > lookupGE 6 (fromList [(3,'a'), (5,'b')]) == Nothing
O(log n). Find smallest element greater or equal to the given one. > lookupGE 3 (fromList [3, 5]) == Just 3 > lookupGE 4 (fromList [3, 5]) == Just 5 > lookupGE 6 (fromList [3, 5]) == Nothing
O(log n). Find smallest key greater or equal to the given one and return the corresponding (key, value) pair. > lookupGE 3 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a') > lookupGE 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b') > lookupGE 6 (fromList [(3,'a'), (5,'b')]) == Nothing
O(log n). Find smallest element greater than the given one. > lookupGT 4 (fromList [3, 5]) == Just 5 > lookupGT 5 (fromList [3, 5]) == Nothing
O(log n). Find smallest key greater than the given one and return the corresponding (key, value) pair. > lookupGT 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b') > lookupGT 5 (fromList [(3,'a'), (5,'b')]) == Nothing
O(log n). Find smallest element greater than the given one. > lookupGT 4 (fromList [3, 5]) == Just 5 > lookupGT 5 (fromList [3, 5]) == Nothing
O(log n). Find smallest key greater than the given one and return the corresponding (key, value) pair. > lookupGT 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b') > lookupGT 5 (fromList [(3,'a'), (5,'b')]) == Nothing
O(log n). Lookup the index of a key. The index is a number from 0 up to, but not including, the size of the map. > isJust (lookupIndex 2 (fromList [(5,"a"), (3,"b")])) == False > fromJust (lookupIndex 3 (fromList [(5,"a"), (3,"b")])) == 0 > fromJust (lookupIndex 5 (fromList [(5,"a"), (3,"b")])) == 1 > isJust (lookupIndex 6 (fromList [(5,"a"), (3,"b")])) == False
O(log n). Find largest element smaller or equal to the given one. > lookupLE 2 (fromList [3, 5]) == Nothing > lookupLE 4 (fromList [3, 5]) == Just 3 > lookupLE 5 (fromList [3, 5]) == Just 5
O(log n). Find largest key smaller or equal to the given one and return the corresponding (key, value) pair. > lookupLE 2 (fromList [(3,'a'), (5,'b')]) == Nothing > lookupLE 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a') > lookupLE 5 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
O(log n). Find largest element smaller or equal to the given one. > lookupLE 2 (fromList [3, 5]) == Nothing > lookupLE 4 (fromList [3, 5]) == Just 3 > lookupLE 5 (fromList [3, 5]) == Just 5
O(log n). Find largest key smaller or equal to the given one and return the corresponding (key, value) pair. > lookupLE 2 (fromList [(3,'a'), (5,'b')]) == Nothing > lookupLE 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a') > lookupLE 5 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
O(log n). Find largest element smaller than the given one. > lookupLT 3 (fromList [3, 5]) == Nothing > lookupLT 5 (fromList [3, 5]) == Just 3
O(log n). Find largest key smaller than the given one and return the corresponding (key, value) pair. > lookupLT 3 (fromList [(3,'a'), (5,'b')]) == Nothing > lookupLT 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
O(log n). Find largest element smaller than the given one. > lookupLT 3 (fromList [3, 5]) == Nothing > lookupLT 5 (fromList [3, 5]) == Just 3
O(log n). Find largest key smaller than the given one and return the corresponding (key, value) pair. > lookupLT 3 (fromList [(3,'a'), (5,'b')]) == Nothing > lookupLT 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
O(min(n,W)). The expression (insertLookupWithKey f k x map) is a pair (lookup k map) and the second element equal to (insertWithKey f k x map). > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value > insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:xxx|a")]) > insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == (Nothing, fromList [(3, "b"), (5, "a"), (7, "xxx")]) > insertLookupWithKey f 5 "xxx" empty == (Nothing, singleton 5 "xxx") This is how to define insertLookup using insertLookupWithKey: > let insertLookup kx x t = insertLookupWithKey (\_ a _ -> a) kx x t > insertLookup 5 "x" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "x")]) > insertLookup 7 "x" (fromList [(5,"a"), (3,"b")]) == (Nothing, fromList [(3, "b"), (5, "a"), (7, "x")])