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-- File created: 2009-01-30 14:54:14
module System.FilePath.Glob.Simplify (simplify) where
import System.FilePath.Glob.Base (Pattern(..), Token(..), liftP)
-- |Simplifies a 'Pattern' object: removes redundant @\"./\"@, for instance.
-- The resulting 'Pattern' matches the exact same input as the original one,
-- with some differences:
--
-- * The output of 'globDir' will differ: for example, globbing for @\"./\*\"@
-- gives @\"./foo\"@, but after simplification this'll be only @\"foo\"@.
--
-- * Decompiling the simplified 'Pattern' will obviously not give the original.
--
-- * The simplified 'Pattern' is a bit faster to match with and uses less
-- memory, since some redundant data is removed.
--
-- For the last of the above reasons, if you're performance-conscious and not
-- using 'globDir', you should always 'simplify' after calling 'compile'.
simplify :: Pattern -> Pattern
simplify = liftP (go . pre)
where
-- ./ at beginning -> nothing (any number of /'s)
pre (ExtSeparator:PathSeparator:xs) = pre (dropWhile isSlash xs)
pre xs = xs
go [] = []
-- /./ -> /
go (PathSeparator:ExtSeparator:xs@(PathSeparator:_)) = go xs
go (x:xs) =
if isSlash x
then let (compressed,ys) = span isSlash xs
in if null compressed
then x : go ys
else go (x : ys)
else x : go xs
isSlash PathSeparator = True
isSlash _ = False
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