[project @ 2001-07-24 16:09:48 by simonpj]

[ghc-hetmet.git] / ghc / lib / std / List.lhs

diff --git a/ghc/lib/std/List.lhs b/ghc/lib/std/List.lhs
index f86c69c..93640a4 100644 (file)
--- a/ghc/lib/std/List.lhs
+++ b/ghc/lib/std/List.lhs
@@ -1,10 +1,10 @@
 % -----------------------------------------------------------------------------
-% $Id: List.lhs,v 1.10 2000/06/30 13:39:35 simonmar Exp $
+% $Id: List.lhs,v 1.12 2001/06/25 13:13:58 simonpj Exp $
 %
 % (c) The University of Glasgow, 1994-2000
 %
 
-\section[List]{Module @Lhar@}
+\section[List]{Module @List@}
 
 \begin{code}
 module List 
@@ -209,14 +209,18 @@ nubBy eq (x:xs)         =  x : nubBy eq (filter (\ y -> not (eq x y)) xs)
 nubBy eq l              = nubBy' l []
   where
     nubBy' [] _                = []
-    nubBy' (x:xs) ls
-       | elemBy eq x ls = nubBy' xs ls 
-       | otherwise     = x : nubBy' xs (x:ls)
-
---not exported:
-elemBy :: (a -> a -> Bool) -> a -> [a] -> Bool
-elemBy _  _ []         =  False
-elemBy eq x (y:ys)     =  x `eq` y || elemBy eq x ys
+    nubBy' (y:ys) xs
+       | elem_by eq y xs = nubBy' ys xs 
+       | otherwise      = y : nubBy' ys (y:xs)
+
+-- Not exported:
+-- Note that we keep the call to `eq` with arguments in the
+-- same order as in the reference implementation
+-- 'xs' is the list of things we've seen so far, 
+-- 'y' is the potential new element
+elem_by :: (a -> a -> Bool) -> a -> [a] -> Bool
+elem_by _  _ []                =  False
+elem_by eq y (x:xs)    =  x `eq` y || elem_by eq y xs
 #endif