diff options
Diffstat (limited to 'compiler/utils/Util.lhs')
| -rw-r--r-- | compiler/utils/Util.lhs | 31 |
1 files changed, 27 insertions, 4 deletions
diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs index 90a2077c71..5c82c757aa 100644 --- a/compiler/utils/Util.lhs +++ b/compiler/utils/Util.lhs @@ -14,11 +14,11 @@ module Util ( -- * General list processing zipEqual, zipWithEqual, zipWith3Equal, zipWith4Equal, - zipLazy, stretchZipWith, + zipLazy, stretchZipWith, zipWithAndUnzip, unzipWith, - mapFst, mapSnd, + mapFst, mapSnd, chkAppend, mapAndUnzip, mapAndUnzip3, mapAccumL2, nOfThem, filterOut, partitionWith, splitEithers, @@ -259,6 +259,13 @@ splitEithers (e : es) = case e of Left x -> (x:xs, ys) Right y -> (xs, y:ys) where (xs,ys) = splitEithers es + +chkAppend :: [a] -> [a] -> [a] +-- Checks for the second arguemnt being empty +-- Used in situations where that situation is common +chkAppend xs ys + | null ys = xs + | otherwise = xs ++ ys \end{code} A paranoid @zip@ (and some @zipWith@ friends) that checks the lists @@ -344,6 +351,14 @@ mapAndUnzip3 f (x:xs) in (r1:rs1, r2:rs2, r3:rs3) +zipWithAndUnzip :: (a -> b -> (c,d)) -> [a] -> [b] -> ([c],[d]) +zipWithAndUnzip f (a:as) (b:bs) + = let (r1, r2) = f a b + (rs1, rs2) = zipWithAndUnzip f as bs + in + (r1:rs1, r2:rs2) +zipWithAndUnzip _ _ _ = ([],[]) + mapAccumL2 :: (s1 -> s2 -> a -> (s1, s2, b)) -> s1 -> s2 -> [a] -> (s1, s2, [b]) mapAccumL2 f s1 s2 xs = (s1', s2', ys) where ((s1', s2'), ys) = mapAccumL (\(s1, s2) x -> case f s1 s2 x of @@ -559,7 +574,15 @@ splitAtList (_:xs) (y:ys) = (y:ys', ys'') -- drop from the end of a list dropTail :: Int -> [a] -> [a] -dropTail n = reverse . drop n . reverse +-- Specification: dropTail n = reverse . drop n . reverse +-- Better implemention due to Joachim Breitner +-- http://www.joachim-breitner.de/blog/archives/600-On-taking-the-last-n-elements-of-a-list.html +dropTail n xs + = go (drop n xs) xs + where + go (_:ys) (x:xs) = x : go ys xs + go _ _ = [] -- Stop when ys runs out + -- It'll always run out before xs does snocView :: [a] -> Maybe ([a],a) -- Split off the last element @@ -1088,7 +1111,7 @@ charToC w = hashString :: String -> Int32 hashString = foldl' f golden where f m c = fromIntegral (ord c) * magic + hashInt32 m - magic = 0xdeadbeef + magic = fromIntegral (0xdeadbeef :: Word32) golden :: Int32 golden = 1013904242 -- = round ((sqrt 5 - 1) * 2^32) :: Int32 |