X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FTree.hs;h=5c95f2ab965ca36e187d4a59a66ed9eac026a21b;hb=e9e2a5412bb7cda8d13a063ac403d9f18ac97380;hp=2ba7b1ab0618e04a7eaf7db0d9f81ece1b147617;hpb=715c78df1e7cdd474926cd919f4193fa9d23ab5e;p=ghc-base.git

diff --git a/Data/Tree.hs b/Data/Tree.hs
index 2ba7b1a..5c95f2a 100644
--- a/Data/Tree.hs
+++ b/Data/Tree.hs
@@ -14,16 +14,29 @@
 
 module Data.Tree(
 	Tree(..), Forest,
+	-- * Two-dimensional drawing
 	drawTree, drawForest,
+	-- * Extraction
 	flatten, levels,
+	-- * Building trees
+	unfoldTree, unfoldForest,
+	unfoldTreeM, unfoldForestM,
+	unfoldTreeM_BF, unfoldForestM_BF,
     ) where
 
 #ifdef __HADDOCK__
 import Prelude
 #endif
 
+import Control.Monad
+import Data.Maybe
+import Data.Queue
+
 -- | Multi-way trees, also known as /rose trees/.
-data Tree a   = Node a (Forest a) -- ^ a value and zero or more child trees.
+data Tree a   = Node {
+		rootLabel :: a,		-- ^ label value
+		subForest :: Forest a	-- ^ zero or more child trees
+	}
 #ifndef __HADDOCK__
   deriving (Eq, Read, Show)
 #else /* __HADDOCK__ (which can't figure these out by itself) */
@@ -40,38 +53,85 @@ mapTree              :: (a -> b) -> (Tree a -> Tree b)
 mapTree f (Node x ts) = Node (f x) (map (mapTree f) ts)
 
 -- | Neat 2-dimensional drawing of a tree.
-drawTree :: Show a => Tree a -> String
-drawTree  = unlines . draw . mapTree show
+drawTree :: Tree String -> String
+drawTree  = unlines . draw
 
 -- | Neat 2-dimensional drawing of a forest.
-drawForest :: Show a => Forest a -> String
+drawForest :: Forest String -> String
 drawForest  = unlines . map drawTree
 
 draw :: Tree String -> [String]
-draw (Node x ts0) = grp this (space (length this)) (stLoop ts0)
- where this          = s1 ++ x ++ " "
-
-       space n       = replicate n ' '
-
-       stLoop []     = [""]
-       stLoop [t]    = grp s2 "  " (draw t)
-       stLoop (t:ts) = grp s3 s4 (draw t) ++ [s4] ++ rsLoop ts
-
-       rsLoop []     = error "rsLoop:Unexpected empty list."
-       rsLoop [t]    = grp s5 "  " (draw t)
-       rsLoop (t:ts) = grp s6 s4 (draw t) ++ [s4] ++ rsLoop ts
+draw (Node x ts0) = x : drawSubTrees ts0
+  where drawSubTrees [] = []
+	drawSubTrees [t] =
+		"|" : shift "`- " "   " (draw t)
+	drawSubTrees (t:ts) =
+		"|" : shift "+- " "|  " (draw t) ++ drawSubTrees ts
 
-       grp fst0 rst  = zipWith (++) (fst0:repeat rst)
-
-       [s1,s2,s3,s4,s5,s6] = ["- ", "--", "-+", " |", " `", " +"]
+	shift first other = zipWith (++) (first : repeat other)
 
 -- | The elements of a tree in pre-order.
 flatten :: Tree a -> [a]
 flatten t = squish t []
- where squish (Node x ts) xs = x:foldr squish xs ts
+  where squish (Node x ts) xs = x:foldr squish xs ts
 
 -- | Lists of nodes at each level of the tree.
 levels :: Tree a -> [[a]]
-levels t = map (map root) $ takeWhile (not . null) $ iterate subforest [t]
- where root (Node x _) = x
-       subforest f     = [t | Node _ ts <- f, t <- ts]
+levels t = map (map rootLabel) $
+		takeWhile (not . null) $
+		iterate (concatMap subForest) [t]
+
+-- | Build a tree from a seed value
+unfoldTree :: (b -> (a, [b])) -> b -> Tree a
+unfoldTree f b = let (a, bs) = f b in Node a (unfoldForest f bs)
+
+-- | Build a forest from a list of seed values
+unfoldForest :: (b -> (a, [b])) -> [b] -> Forest a
+unfoldForest f = map (unfoldTree f)
+
+-- | Monadic tree builder, in depth-first order
+unfoldTreeM :: Monad m => (b -> m (a, [b])) -> b -> m (Tree a)
+unfoldTreeM f b = do
+	(a, bs) <- f b
+	ts <- unfoldForestM f bs
+	return (Node a ts)
+
+-- | Monadic forest builder, in depth-first order
+#ifndef __NHC__
+unfoldForestM :: Monad m => (b -> m (a, [b])) -> [b] -> m (Forest a)
+#endif
+unfoldForestM f = mapM (unfoldTreeM f)
+
+-- | Monadic tree builder, in breadth-first order,
+-- using an algorithm adapted from
+-- /Breadth-First Numbering: Lessons from a Small Exercise in Algorithm Design/,
+-- by Chris Okasaki, /ICFP'00/.
+unfoldTreeM_BF :: Monad m => (b -> m (a, [b])) -> b -> m (Tree a)
+unfoldTreeM_BF f b = liftM (fst . fromJust . deQueue) $
+	unfoldForestQ f (listToQueue [b])
+
+-- | Monadic forest builder, in breadth-first order,
+-- using an algorithm adapted from
+-- /Breadth-First Numbering: Lessons from a Small Exercise in Algorithm Design/,
+-- by Chris Okasaki, /ICFP'00/.
+unfoldForestM_BF :: Monad m => (b -> m (a, [b])) -> [b] -> m (Forest a)
+unfoldForestM_BF f = liftM (reverseOnto []) . unfoldForestQ f . listToQueue
+  where reverseOnto :: [a'] -> Queue a' -> [a']
+	reverseOnto as q = case deQueue q of
+		Nothing -> as
+		Just (a, q') -> reverseOnto (a:as) q'
+
+-- takes a queue of seeds
+-- produces a queue of trees of the same length, but in the reverse order
+unfoldForestQ :: Monad m => (b -> m (a, [b])) -> Queue b -> m (Queue (Tree a))
+unfoldForestQ f aQ = case deQueue aQ of
+	Nothing -> return emptyQueue
+	Just (a, aQ) -> do
+		(b, as) <- f a
+		tQ <- unfoldForestQ f (foldl addToQueue aQ as)
+		let (ts, tQ') = splitOnto [] as tQ
+		return (addToQueue tQ' (Node b ts))
+  where splitOnto :: [a'] -> [b'] -> Queue a' -> ([a'], Queue a')
+	splitOnto as [] q = (as, q)
+	splitOnto as (_:bs) q = case fromJust (deQueue q) of
+		(a, q') -> splitOnto (a:as) bs q'