# Difference between revisions of "The Monad.Reader/Discuss Issue11/FingerTreeIMap"

From HaskellWiki

m |
Tomjaguarpaw (talk | contribs) (Deleting page that hasn't been updated for over 10 years) |
||

Line 1: | Line 1: | ||

− | --[[User:Dfplace|Dfplace]] 16:19, 12 September 2008 (UTC) |
||

− | |||

− | <haskell> |
||

− | {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-} |
||

− | module IMap where |
||

− | import Data.FingerTree |
||

− | import Data.List hiding (insert,delete,lookup) |
||

− | import Prelude hiding (lookup) |
||

− | import Data.Monoid |
||

− | |||

− | data Elem a b = Elem a b |
||

− | |||

− | data Key k v = NoKey | Key k v |
||

− | |||

− | instance Eq k => Eq (Key k v) where |
||

− | (Key j _) == (Key k _) = j == k |
||

− | NoKey == NoKey = True |
||

− | NoKey == (Key _ _) = False |
||

− | (Key _ _) == NoKey = False |
||

− | |||

− | instance Ord k => Ord (Key k v) where |
||

− | compare (Key j _) (Key k _) = compare j k |
||

− | compare NoKey NoKey = EQ |
||

− | compare (Key _ _) NoKey = GT |
||

− | compare NoKey (Key _ _ ) = LT |
||

− | |||

− | instance Monoid v => Monoid (Key a v) where |
||

− | mempty = NoKey |
||

− | k `mappend` NoKey = k |
||

− | NoKey `mappend` k = k |
||

− | (Key _ x) `mappend` (Key k y) = Key k (x `mappend` y) |
||

− | |||

− | data IMap a b = IMap (FingerTree (Key a b) (Elem a b)) |
||

− | |||

− | instance (Monoid b) => Measured (Key a b) (Elem a b) where |
||

− | measure (Elem x y) = Key x y |
||

− | |||

− | insert :: (Ord k, Monoid v) => k -> v -> IMap k v -> IMap k v |
||

− | insert k v (IMap xs) = insert' $ viewl r |
||

− | where |
||

− | (l,r) = split (>= Key k undefined) xs |
||

− | new = IMap ( l >< (Elem k v <| r)) |
||

− | insert' ((Elem y _) :< r') |
||

− | | k == y = IMap ( l >< (Elem k v <| r')) |
||

− | | otherwise = new |
||

− | insert' EmptyL = new |
||

− | |||

− | delete :: (Ord k, Monoid v) => k -> IMap k v -> IMap k v |
||

− | delete x (IMap xs) = IMap (l >< r') |
||

− | where |
||

− | (l,r) = split (>= Key x undefined) xs |
||

− | (_,r') = split (> Key x undefined) r |
||

− | |||

− | lookup :: (Monad m, Ord t, Monoid v) => t -> IMap t v -> m v |
||

− | lookup x (IMap xs) = lookup' $ |
||

− | viewl . snd $ |
||

− | split (>= Key x undefined) xs |
||

− | where |
||

− | lookup' ((Elem y v) :< _) |
||

− | | y == x = return v |
||

− | | otherwise = fail "IMap.lookup failed" |
||

− | lookup' EmptyL = fail "IMap.lookup failed" |
||

− | |||

− | getValue :: (Monoid v) => IMap k v -> v |
||

− | getValue (IMap xs) = let (Key _ v) = measure xs in v |
||

− | </haskell> |