X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FDigraph.lhs;h=f80b33f870517806b8e8a48714b91c25d803a470;hb=47adb8b6c491df7e51fd34e6bb45dfe3d6fe681a;hp=cde008ad9a2307490c26ac88c3f47b1c34b8af18;hpb=9ec880fcb29ff038bcc72d78bbe2fd6933566047;p=ghc-hetmet.git

diff --git a/compiler/utils/Digraph.lhs b/compiler/utils/Digraph.lhs
index cde008a..f80b33f 100644
--- a/compiler/utils/Digraph.lhs
+++ b/compiler/utils/Digraph.lhs
@@ -3,6 +3,13 @@
 %
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module Digraph(
 
         -- At present the only one with a "nice" external interface
@@ -76,6 +83,16 @@ instance Outputable a => Outputable (SCC a) where
    ppr (CyclicSCC vs) = text "REC" $$ (nest 3 (vcat (map ppr vs)))
 \end{code}
 
+Note [Nodes, keys, vertices]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * A 'node' is a big blob of client-stuff
+
+ * Each 'node' has a unique (client) 'key', but the latter 
+	is in Ord and has fast comparison
+
+ * Digraph then maps each 'key' to a Vertex (Int) which is
+  	arranged densely in 0.n
+
 \begin{code}
 stronglyConnComp
         :: Ord key
@@ -323,17 +340,17 @@ preArr bnds      = tabulate bnds . preorderF
 ------------------------------------------------------------
 
 \begin{code}
---postorder :: Tree a -> [a]
-postorder (Node a ts) = postorderF ts ++ [a]
+postorder :: Tree a -> [a] -> [a]
+postorder (Node a ts) = postorderF ts . (a :)
 
-postorderF   :: Forest a -> [a]
-postorderF ts = concat (map postorder ts)
+postorderF   :: Forest a -> [a] -> [a]
+postorderF ts = foldr (.) id $ map postorder ts
 
-postOrd      :: Graph -> [Vertex]
-postOrd       = postorderF . dff
+postOrd :: Graph -> [Vertex]
+postOrd g = postorderF (dff g) []
 
-topSort      :: Graph -> [Vertex]
-topSort       = reverse . postOrd
+topSort :: Graph -> [Vertex]
+topSort = reverse . postOrd
 \end{code}