Add min/max handling operations for IntSet/IntMap

[haskell-directory.git] / Data / Map.hs

diff --git a/Data/Map.hs b/Data/Map.hs
index 56b25e1..399f74c 100644 (file)
--- a/Data/Map.hs
+++ b/Data/Map.hs
@@ -11,10 +11,11 @@
 --
 -- An efficient implementation of maps from keys to values (dictionaries).
 --
--- This module is intended to be imported @qualified@, to avoid name
--- clashes with Prelude functions.  eg.
+-- Since many function names (but not the type name) clash with
+-- "Prelude" names, this module is usually imported @qualified@, e.g.
 --
--- >  import Data.Map as Map
+-- >  import Data.Map (Map)
+-- >  import qualified Data.Map as Map
 --
 -- The implementation of 'Map' is based on /size balanced/ binary trees (or
 -- trees of /bounded balance/) as described by:
@@ -55,6 +56,7 @@ module Data.Map  (
             -- ** Insertion
             , insert
             , insertWith, insertWithKey, insertLookupWithKey
+            , insertWith', insertWithKey'
             
             -- ** Delete\/Update
             , delete
@@ -155,6 +157,8 @@ module Data.Map  (
             , updateMaxWithKey
             , minView
             , maxView
+            , minViewWithKey
+            , maxViewWithKey
             
             -- * Debugging
             , showTree
@@ -249,7 +253,12 @@ size t
       Bin sz k x l r  -> sz
 
 
--- | /O(log n)/. Lookup the value at a key in the map.
+-- | /O(log n)/. Lookup the value at a key in the map. 
+--
+-- The function will 
+-- @return@ the result in the monad or @fail@ in it the key isn't in the 
+-- map. Often, the monad to use is 'Maybe', so you get either 
+-- @('Just' result)@ or @'Nothing'@.
 lookup :: (Monad m,Ord k) => k -> Map k a -> m a
 lookup k t = case lookup' k t of
     Just x -> return x
@@ -342,6 +351,12 @@ insertWith :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
 insertWith f k x m          
   = insertWithKey (\k x y -> f x y) k x m
 
+-- | Same as 'insertWith', but the combining function is applied strictly.
+insertWith' :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWith' f k x m          
+  = insertWithKey' (\k x y -> f x y) k x m
+
+
 -- | /O(log n)/. Insert with a combining function.
 -- @'insertWithKey' f key value mp@ 
 -- will insert the pair (key, value) into @mp@ if key does
@@ -358,6 +373,18 @@ insertWithKey f kx x t
                GT -> balance ky y l (insertWithKey f kx x r)
                EQ -> Bin sy kx (f kx x y) l r
 
+-- | Same as 'insertWithKey', but the combining function is applied strictly.
+insertWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWithKey' f kx x t
+  = case t of
+      Tip -> singleton kx x
+      Bin sy ky y l r
+          -> case compare kx ky of
+               LT -> balance ky y (insertWithKey' f kx x l) r
+               GT -> balance ky y l (insertWithKey' f kx x r)
+               EQ -> let x' = f kx x y in seq x' (Bin sy kx x' l r)
+
+
 -- | /O(log n)/. The expression (@'insertLookupWithKey' f k x map@)
 -- is a pair where the first element is equal to (@'lookup' k map@)
 -- and the second element equal to (@'insertWithKey' f k x map@).
@@ -569,19 +596,33 @@ updateMaxWithKey f t
       Bin sx kx x l r    -> balance kx x l (updateMaxWithKey f r)
       Tip                -> Tip
 
--- | /O(log n)/. Retrieves the minimal key of the map, and the map stripped from that element
+-- | /O(log n)/. Retrieves the minimal (key,value) pair of the map, and the map stripped from that element
+-- @fail@s (in the monad) when passed an empty map.
+minViewWithKey :: Monad m => Map k a -> m ((k,a), Map k a)
+minViewWithKey Tip = fail "Map.minView: empty map"
+minViewWithKey x = return (deleteFindMin x)
+
+-- | /O(log n)/. Retrieves the maximal (key,value) pair of the map, and the map stripped from that element
+-- @fail@s (in the monad) when passed an empty map.
+maxViewWithKey :: Monad m => Map k a -> m ((k,a), Map k a)
+maxViewWithKey Tip = fail "Map.maxView: empty map"
+maxViewWithKey x = return (deleteFindMax x)
+
+-- | /O(log n)/. Retrieves the minimal key\'s value of the map, and the map stripped from that element
 -- @fail@s (in the monad) when passed an empty map.
-minView :: Monad m => Map k a -> m (Map k a, (k,a))
+minView :: Monad m => Map k a -> m (a, Map k a)
 minView Tip = fail "Map.minView: empty map"
-minView x = return (swap $ deleteFindMin x)
+minView x = return (first snd $ deleteFindMin x)
 
--- | /O(log n)/. Retrieves the maximal key of the map, and the map stripped from that element
+-- | /O(log n)/. Retrieves the maximal key\'s value of the map, and the map stripped from that element
 -- @fail@s (in the monad) when passed an empty map.
-maxView :: Monad m => Map k a -> m (Map k a, (k,a))
+maxView :: Monad m => Map k a -> m (a, Map k a)
 maxView Tip = fail "Map.maxView: empty map"
-maxView x = return (swap $ deleteFindMax x)
+maxView x = return (first snd $ deleteFindMax x)
 
-swap (a,b) = (b,a)
+-- Update the 1st component of a tuple (special case of Control.Arrow.first)
+first :: (a -> b) -> (a,c) -> (b,c)
+first f (x,y) = (f x, y)
 
 {--------------------------------------------------------------------
   Union.