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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2013-08-16 11:15:33 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2013-08-19 09:46:10 +0100 |
| commit | 098c7d1786d58bb9d2a6e1297707489488588d75 (patch) | |
| tree | 466e3dbaf5882de594bb9af1d94e6ba620ee8ea1 /compiler/utils/Util.lhs | |
| parent | 83440fdc4f1b52b2f398326e0e86d4583afa433a (diff) | |
| download | haskell-098c7d1786d58bb9d2a6e1297707489488588d75.tar.gz | |
Add a better implementation of dropTail, and use it
Diffstat (limited to 'compiler/utils/Util.lhs')
| -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 |