-}
+{-
+
+Copyright (C) 2009 Google Inc.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+-}
+
module Ganeti.HTools.PeerMap
- (
- PeerMap,
- Key,
- Elem,
- empty,
- create,
- accumArray,
- Ganeti.HTools.PeerMap.find,
- add,
- remove,
- maxElem
+ ( PeerMap
+ , Key
+ , Elem
+ , empty
+ , accumArray
+ , Ganeti.HTools.PeerMap.find
+ , add
+ , remove
+ , maxElem
) where
import Data.Maybe (fromMaybe)
import Data.List
-import Data.Function
-import Data.Ord
+import Data.Ord (comparing)
import Ganeti.HTools.Types
type Elem = Int
type PeerMap = [(Key, Elem)]
+-- * Initialization functions
+
+-- | Create a new empty map.
empty :: PeerMap
empty = []
-create :: Key -> PeerMap
-create _ = []
-
--- | Our reverse-compare function
+-- | Our reverse-compare function.
pmCompare :: (Key, Elem) -> (Key, Elem) -> Ordering
-pmCompare a b = (compare `on` snd) b a
+pmCompare a b = comparing snd b a
+-- | Add or update (via a custom function) an element.
addWith :: (Elem -> Elem -> Elem) -> Key -> Elem -> PeerMap -> PeerMap
addWith fn k v lst =
- let r = lookup k lst
- in
- case r of
- Nothing -> insertBy pmCompare (k, v) lst
- Just o -> insertBy pmCompare (k, fn o v) (remove k lst)
-
-accumArray :: (Elem -> Elem -> Elem) -> Elem -> (Key, Key) ->
- [(Key, Elem)] -> PeerMap
-accumArray fn _ _ lst =
- case lst of
- [] -> empty
- (k, v):xs -> addWith fn k v $ accumArray fn undefined undefined xs
+ case lookup k lst of
+ Nothing -> insertBy pmCompare (k, v) lst
+ Just o -> insertBy pmCompare (k, fn o v) (remove k lst)
+
+-- | Create a PeerMap from an association list, with possible duplicates
+accumArray :: (Elem -> Elem -> Elem) -- ^ function used to merge the elements
+ -> [(Key, Elem)] -- ^ source data
+ -> PeerMap -- ^ results
+accumArray _ [] = empty
+accumArray fn ((k, v):xs) = addWith fn k v $ accumArray fn xs
+-- * Basic operations
+
+-- | Returns either the value for a key or zero if not found
find :: Key -> PeerMap -> Elem
-find k c = fromMaybe 0 $ lookup k c
+find k = fromMaybe 0 . lookup k
+-- | Add an element to a peermap, overwriting the previous value
add :: Key -> Elem -> PeerMap -> PeerMap
-add k v c = addWith (\_ n -> n) k v c
+add = addWith (flip const)
+-- | Remove an element from a peermap
remove :: Key -> PeerMap -> PeerMap
-remove k c = case c of
- [] -> []
- (x@(x', _)):xs -> if k == x' then xs
- else x:(remove k xs)
-
-to_list :: PeerMap -> [Elem]
-to_list c = snd $ unzip c
-
+remove _ [] = []
+remove k ((x@(x', _)):xs) = if k == x'
+ then xs
+ else x:remove k xs
+
+-- | Find the maximum element.
+--
+-- Since this is a sorted list, we just get the value at the head of
+-- the list, or zero for a null list
maxElem :: PeerMap -> Elem
-maxElem c = case c of
- [] -> 0
- (_, v):_ -> v
+maxElem (x:_) = snd x
+maxElem _ = 0