[project @ 2001-09-08 21:42:07 by sof]

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

diff --git a/ghc/lib/std/List.lhs b/ghc/lib/std/List.lhs
index 709687a..4633099 100644 (file)
--- a/ghc/lib/std/List.lhs
+++ b/ghc/lib/std/List.lhs
@@ -1,8 +1,10 @@
+% -----------------------------------------------------------------------------
+% $Id: List.lhs,v 1.13 2001/08/29 10:12:34 simonmar Exp $
 %
-% (c) The AQUA Project, Glasgow University, 1994-1999
+% (c) The University of Glasgow, 1994-2000
 %
 
-\section[List]{Module @Lhar@}
+\section[List]{Module @List@}
 
 \begin{code}
 module List 
@@ -65,7 +67,7 @@ module List
    , genericIndex      -- :: (Integral a) => [b] -> a -> b
    , genericReplicate  -- :: (Integral a) => a -> b -> [b]
    
-   , unfoldr           -- :: (a -> Maybe (b,a)) -> a -> (a,[b])
+   , unfoldr           -- :: (b -> Maybe (a, b)) -> b -> [a]
 
    , zip4, zip5, zip6, zip7
    , zipWith4, zipWith5, zipWith6, zipWith7
@@ -207,14 +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
 
 
@@ -317,13 +323,21 @@ insertBy cmp x ys@(y:ys')
      GT -> y : insertBy cmp x ys'
      _  -> x : ys
 
-maximumBy              :: (a -> a -> a) -> [a] -> a
-maximumBy _   []       =  error "List.maximumBy: empty list"
-maximumBy max xs       =  foldl1 max xs
-
-minimumBy              :: (a -> a -> a) -> [a] -> a
-minimumBy _   []       =  error "List.minimumBy: empty list"
-minimumBy min xs       =  foldl1 min xs
+maximumBy              :: (a -> a -> Ordering) -> [a] -> a
+maximumBy _ []         =  error "List.maximumBy: empty list"
+maximumBy cmp xs       =  foldl1 max xs
+                       where
+                          max x y = case cmp x y of
+                                       GT -> x
+                                       _  -> y
+
+minimumBy              :: (a -> a -> Ordering) -> [a] -> a
+minimumBy _ []         =  error "List.minimumBy: empty list"
+minimumBy cmp xs       =  foldl1 min xs
+                       where
+                          min x y = case cmp x y of
+                                       GT -> y
+                                       _  -> x
 
 genericLength           :: (Num i) => [b] -> i
 genericLength []        =  0