X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Flib%2Fstd%2FPrelList.lhs;h=3a7ce28710dab5c41d3aea096dabf5868cfe7f80;hb=88f53e66a48db654fcc60f3d72cdedd78b6c7079;hp=496aa1ea1215f1baabb17886e588fd3cdb4ab6ab;hpb=8f918dc1e7c36c97a37fbf6559b1bcbecb31b4af;p=ghc-hetmet.git diff --git a/ghc/lib/std/PrelList.lhs b/ghc/lib/std/PrelList.lhs index 496aa1e..3a7ce28 100644 --- a/ghc/lib/std/PrelList.lhs +++ b/ghc/lib/std/PrelList.lhs @@ -1,5 +1,5 @@ % ------------------------------------------------------------------------------ -% $Id: PrelList.lhs,v 1.21 2000/08/29 16:35:56 simonpj Exp $ +% $Id: PrelList.lhs,v 1.27 2001/08/28 15:12:37 simonmar Exp $ % % (c) The University of Glasgow, 1994-2000 % @@ -157,9 +157,15 @@ filterList pred (x:xs) -- scanl1 is similar, again without the starting element: -- scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...] -foldl :: (a -> b -> a) -> a -> [b] -> a -foldl _ z [] = z -foldl f z (x:xs) = foldl f (f z x) xs +-- We write foldl as a non-recursive thing, so that it +-- can be inlined, and then (often) strictness-analysed, +-- and hence the classic space leak on foldl (+) 0 xs + +foldl :: (a -> b -> a) -> a -> [b] -> a +foldl f z xs = lgo z xs + where + lgo z [] = z + lgo z (x:xs) = lgo (f z x) xs foldl1 :: (a -> a -> a) -> [a] -> a foldl1 f (x:xs) = foldl f x xs @@ -170,9 +176,9 @@ scanl f q ls = q : (case ls of [] -> [] x:xs -> scanl f (f q x) xs) -scanl1 :: (a -> a -> a) -> [a] -> [a] -scanl1 f (x:xs) = scanl f x xs -scanl1 _ [] = errorEmptyList "scanl1" +scanl1 :: (a -> a -> a) -> [a] -> [a] +scanl1 f (x:xs) = scanl f x xs +scanl1 _ [] = [] -- foldr, foldr1, scanr, and scanr1 are the right-to-left duals of the -- above functions. @@ -188,10 +194,10 @@ scanr f q0 (x:xs) = f x q : qs where qs@(q:_) = scanr f q0 xs scanr1 :: (a -> a -> a) -> [a] -> [a] -scanr1 _ [x] = [x] -scanr1 f (x:xs) = f x q : qs +scanr1 f [] = [] +scanr1 f [x] = [x] +scanr1 f (x:xs) = f x q : qs where qs@(q:_) = scanr1 f xs -scanr1 _ [] = errorEmptyList "scanr1" -- iterate f x returns an infinite list of repeated applications of f to x: -- iterate f x == [x, f x, f (f x), ...] @@ -255,23 +261,17 @@ dropWhile p xs@(x:xs') -- is equivalent to (take n xs, drop n xs). #ifdef USE_REPORT_PRELUDE take :: Int -> [a] -> [a] -take 0 _ = [] +take n _ | n <= 0 = [] take _ [] = [] -take n (x:xs) | n > 0 = x : take (minusInt n 1) xs -take _ _ = errorNegativeIdx "take" +take n (x:xs) = x : take (n-1) xs drop :: Int -> [a] -> [a] -drop 0 xs = xs +drop n xs | n <= 0 = xs drop _ [] = [] -drop n (_:xs) | n > 0 = drop (minusInt n 1) xs -drop _ _ = errorNegativeIdx "drop" - +drop n (_:xs) = drop (n-1) xs -splitAt :: Int -> [a] -> ([a],[a]) -splitAt 0 xs = ([],xs) -splitAt _ [] = ([],[]) -splitAt n (x:xs) | n > 0 = (x:xs',xs'') where (xs',xs'') = splitAt (minusInt n 1) xs -splitAt _ _ = errorNegativeIdx "splitAt" +splitAt :: Int -> [a] -> ([a],[a]) +splitAt n xs = (take n xs, drop n xs) #else /* hack away */ take :: Int -> [b] -> [b] @@ -284,7 +284,7 @@ take (I# n#) xs = takeUInt n# xs takeUInt :: Int# -> [b] -> [b] takeUInt n xs | n >=# 0# = take_unsafe_UInt n xs - | otherwise = errorNegativeIdx "take" + | otherwise = [] take_unsafe_UInt :: Int# -> [b] -> [b] take_unsafe_UInt 0# _ = [] @@ -296,7 +296,7 @@ take_unsafe_UInt m ls = takeUInt_append :: Int# -> [b] -> [b] -> [b] takeUInt_append n xs rs | n >=# 0# = take_unsafe_UInt_append n xs rs - | otherwise = errorNegativeIdx "take" + | otherwise = [] take_unsafe_UInt_append :: Int# -> [b] -> [b] -> [b] take_unsafe_UInt_append 0# _ rs = rs @@ -307,7 +307,7 @@ take_unsafe_UInt_append m ls rs = drop :: Int -> [b] -> [b] drop (I# n#) ls - | n# <# 0# = errorNegativeIdx "drop" + | n# <# 0# = [] | otherwise = drop# n# ls where drop# :: Int# -> [a] -> [a] @@ -317,7 +317,7 @@ drop (I# n#) ls splitAt :: Int -> [b] -> ([b], [b]) splitAt (I# n#) ls - | n# <# 0# = errorNegativeIdx "splitAt" + | n# <# 0# = ([], ls) | otherwise = splitAt# n# ls where splitAt# :: Int# -> [a] -> ([a], [a]) @@ -435,8 +435,11 @@ concatMap :: (a -> [b]) -> [a] -> [b] concatMap f = foldr ((++) . f) [] concat :: [[a]] -> [a] -{-# INLINE concat #-} concat = foldr (++) [] + +{-# RULES + "concat" forall xs. concat xs = build (\c n -> foldr (\x y -> foldr c y x) n xs) + #-} \end{code} @@ -444,10 +447,10 @@ concat = foldr (++) [] -- List index (subscript) operator, 0-origin (!!) :: [a] -> Int -> a #ifdef USE_REPORT_PRELUDE -(x:_) !! 0 = x -(_:xs) !! n | n > 0 = xs !! (minusInt n 1) -(_:_) !! _ = error "Prelude.(!!): negative index" -[] !! _ = error "Prelude.(!!): index too large" +xs !! n | n < 0 = error "Prelude.!!: negative index" +[] !! _ = error "Prelude.!!: index too large" +(x:_) !! 0 = x +(_:xs) !! n = xs !! (n-1) #else -- HBC version (stolen), then unboxified -- The semantics is not quite the same for error conditions @@ -506,7 +509,7 @@ I'm going to leave it though. zip takes two lists and returns a list of corresponding pairs. If one input list is short, excess elements of the longer list are discarded. zip3 takes three lists and returns a list of triples. Zips for larger -tuples are in the List library +tuples are in the List module. \begin{code} ---------------------------------------------- @@ -592,10 +595,6 @@ errorEmptyList :: String -> a errorEmptyList fun = error (prel_list_str ++ fun ++ ": empty list") -errorNegativeIdx :: String -> a -errorNegativeIdx fun = - error (prel_list_str ++ fun ++ ": negative index") - prel_list_str :: String prel_list_str = "Prelude." \end{code}