diff options
Diffstat (limited to 'compiler/utils')
| -rw-r--r-- | compiler/utils/Util.lhs | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs index 7292b4a4b3..aa5f6f9c95 100644 --- a/compiler/utils/Util.lhs +++ b/compiler/utils/Util.lhs @@ -23,6 +23,8 @@ module Util ( mapAndUnzip, mapAndUnzip3, mapAccumL2, nOfThem, filterOut, partitionWith, splitEithers, + dropWhileEndLE, + foldl1', foldl2, count, all2, lengthExceeds, lengthIs, lengthAtLeast, @@ -593,6 +595,18 @@ dropTail n xs go _ _ = [] -- Stop when ys runs out -- It'll always run out before xs does +-- dropWhile from the end of a list. This is similar to Data.List.dropWhileEnd, +-- but is lazy in the elements and strict in the spine. For reasonably short lists, +-- such as path names and typical lines of text, dropWhileEndLE is generally +-- faster than dropWhileEnd. Its advantage is magnified when the predicate is +-- expensive--using dropWhileEndLE isSpace to strip the space off a line of text +-- is generally much faster than using dropWhileEnd isSpace for that purpose. +-- Specification: dropWhileEndLE p = reverse . dropWhile p . reverse +-- Pay attention to the short-circuit (&&)! The order of its arguments is the only +-- difference between dropWhileEnd and dropWhileEndLE. +dropWhileEndLE :: (a -> Bool) -> [a] -> [a] +dropWhileEndLE p = foldr (\x r -> if null r && p x then [] else x:r) [] + snocView :: [a] -> Maybe ([a],a) -- Split off the last element snocView [] = Nothing @@ -651,7 +665,7 @@ cmpList cmp (a:as) (b:bs) \begin{code} removeSpaces :: String -> String -removeSpaces = reverse . dropWhile isSpace . reverse . dropWhile isSpace +removeSpaces = dropWhileEndLE isSpace . dropWhile isSpace \end{code} %************************************************************************ |