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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 | |
| parent | 83440fdc4f1b52b2f398326e0e86d4583afa433a (diff) | |
| download | haskell-098c7d1786d58bb9d2a6e1297707489488588d75.tar.gz | |
Add a better implementation of dropTail, and use it
| -rw-r--r-- | compiler/ghci/Linker.lhs | 2 | ||||
| -rw-r--r-- | compiler/utils/Util.lhs | 10 |
2 files changed, 10 insertions, 2 deletions
diff --git a/compiler/ghci/Linker.lhs b/compiler/ghci/Linker.lhs index 45bc9d56c9..192df2ee57 100644 --- a/compiler/ghci/Linker.lhs +++ b/compiler/ghci/Linker.lhs @@ -637,7 +637,7 @@ getLinkDeps hsc_env hpt pls replace_osuf span mods adjust_ul new_osuf (DotO file) = do MASSERT(osuf `isSuffixOf` file) - let file_base = reverse (drop (length osuf + 1) (reverse file)) + let file_base = dropTail (length osuf + 1) file new_file = file_base <.> new_osuf ok <- doesFileExist new_file if (not ok) 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 |