diff options
Diffstat (limited to 'compiler/utils')
| -rw-r--r-- | compiler/utils/Util.lhs | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs index dd947ffd93..5c82c757aa 100644 --- a/compiler/utils/Util.lhs +++ b/compiler/utils/Util.lhs @@ -574,7 +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 |