[commit: ghc] master: Use dropWhileEndLE p instead of reverse . dropWhile p . reverse (2a88568)
git at git.haskell.org
git at git.haskell.org
Wed Oct 1 21:38:52 UTC 2014
Repository : ssh://git@git.haskell.org/ghc
On branch : master
Link : http://ghc.haskell.org/trac/ghc/changeset/2a8856884de7d476e26b4ffa829ccb3a14d6f63e/ghc
>---------------------------------------------------------------
commit 2a8856884de7d476e26b4ffa829ccb3a14d6f63e
Author: David Feuer <David.Feuer at gmail.com>
Date: Wed Oct 1 23:34:29 2014 +0200
Use dropWhileEndLE p instead of reverse . dropWhile p . reverse
Summary: Using `dropWhileEndLE` tends to be faster and easier to read
than the `reverse . dropWhile p . reverse` idiom. This also cleans up
some other, nearby, messes. Fix #9616 (incorrect number formatting
potentially leading to incorrect numbers in output).
Test Plan: Run validate
Reviewers: thomie, rwbarton, nomeata, austin
Reviewed By: nomeata, austin
Subscribers: simonmar, ezyang, carter, thomie
Projects: #ghc
Differential Revision: https://phabricator.haskell.org/D259
GHC Trac Issues: #9623, #9616
Conflicts:
compiler/basicTypes/OccName.lhs
>---------------------------------------------------------------
2a8856884de7d476e26b4ffa829ccb3a14d6f63e
compiler/basicTypes/OccName.lhs | 2 +-
compiler/utils/Util.lhs | 16 +++++++++++++++-
libraries/base/GHC/Windows.hs | 3 ++-
utils/hpc/HpcMarkup.hs | 25 +++++++++++++++++++------
utils/hpc/HpcUtils.hs | 4 ++++
5 files changed, 41 insertions(+), 9 deletions(-)
diff --git a/compiler/basicTypes/OccName.lhs b/compiler/basicTypes/OccName.lhs
index 1f1fda8..0010ad3 100644
--- a/compiler/basicTypes/OccName.lhs
+++ b/compiler/basicTypes/OccName.lhs
@@ -833,7 +833,7 @@ tidyOccName env occ@(OccName occ_sp fs)
Nothing -> (addToUFM env fs 1, occ)
where
base :: String -- Drop trailing digits (see Note [TidyOccEnv])
- base = reverse (dropWhile isDigit (reverse (unpackFS fs)))
+ base = dropWhileEndLE isDigit (unpackFS fs)
find n
= case lookupUFM env new_fs of
diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs
index 7292b4a..aa5f6f9 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}
%************************************************************************
diff --git a/libraries/base/GHC/Windows.hs b/libraries/base/GHC/Windows.hs
index 0a57fc3..83f83df 100644
--- a/libraries/base/GHC/Windows.hs
+++ b/libraries/base/GHC/Windows.hs
@@ -69,6 +69,7 @@ import GHC.Base
import GHC.IO
import GHC.Num
import System.IO.Error
+import Util
import qualified Numeric
@@ -120,7 +121,7 @@ errCodeToIOError fn_name err_code = do
-- XXX we should really do this directly.
let errno = c_maperrno_func err_code
- let msg' = reverse $ dropWhile isSpace $ reverse msg -- drop trailing \n
+ let msg' = dropWhileEndLE isSpace msg -- drop trailing \n
ioerror = errnoToIOError fn_name errno Nothing Nothing
`ioeSetErrorString` msg'
return ioerror
diff --git a/utils/hpc/HpcMarkup.hs b/utils/hpc/HpcMarkup.hs
index 8fd9e42..c294b6a 100644
--- a/utils/hpc/HpcMarkup.hs
+++ b/utils/hpc/HpcMarkup.hs
@@ -140,6 +140,16 @@ charEncodingTag =
"<meta http-equiv=\"Content-Type\" " ++
"content=\"text/html; " ++ "charset=" ++ show localeEncoding ++ "\">"
+-- Add characters to the left of a string until it is at least as
+-- large as requested.
+padLeft :: Int -> Char -> String -> String
+padLeft n c str = go n str
+ where
+ -- If the string is already long enough, stop traversing it.
+ go 0 _ = str
+ go k [] = replicate k c ++ str
+ go k (_:xs) = go (k-1) xs
+
genHtmlFromMod
:: String
-> Flags
@@ -210,8 +220,7 @@ genHtmlFromMod dest_dir flags tix theFunTotals invertOutput = do
content <- readFileFromPath (hpcError markup_plugin) origFile theHsPath
let content' = markup tabStop info content
- let show' = reverse . take 5 . (++ " ") . reverse . show
- let addLine n xs = "<span class=\"lineno\">" ++ show' n ++ " </span>" ++ xs
+ let addLine n xs = "<span class=\"lineno\">" ++ padLeft 5 ' ' (show n) ++ " </span>" ++ xs
let addLines = unlines . map (uncurry addLine) . zip [1 :: Int ..] . lines
let fileName = modName0 ++ ".hs.html"
putStrLn $ "Writing: " ++ fileName
@@ -363,10 +372,14 @@ openTick (TopLevelDecl True 1)
openTick (TopLevelDecl True n0)
= "<span class=\"funcount\">-- entered " ++ showBigNum n0 ++ " times</span>" ++ openTopDecl
where showBigNum n | n <= 9999 = show n
- | otherwise = showBigNum' (n `div` 1000) ++ "," ++ showWith (n `mod` 1000)
+ | otherwise = case n `quotRem` 1000 of
+ (q, r) -> showBigNum' q ++ "," ++ showWith r
showBigNum' n | n <= 999 = show n
- | otherwise = showBigNum' (n `div` 1000) ++ "," ++ showWith (n `mod` 1000)
- showWith n = take 3 $ reverse $ ("000" ++) $ reverse $ show n
+ | otherwise = case n `quotRem` 1000 of
+ (q, r) -> showBigNum' q ++ "," ++ showWith r
+ showWith n = padLeft 3 '0' $ show n
+
+
closeTick :: String
closeTick = "</span>"
@@ -462,7 +475,7 @@ instance Monoid ModuleSummary where
writeFileUsing :: String -> String -> IO ()
writeFileUsing filename text = do
- let dest_dir = reverse . dropWhile (\ x -> x /= '/') . reverse $ filename
+ let dest_dir = dropWhileEndLE (\ x -> x /= '/') $ filename
-- We need to check for the dest_dir each time, because we use sub-dirs for
-- packages, and a single .tix file might contain information about
diff --git a/utils/hpc/HpcUtils.hs b/utils/hpc/HpcUtils.hs
index 5655f83..73d9cd3 100644
--- a/utils/hpc/HpcUtils.hs
+++ b/utils/hpc/HpcUtils.hs
@@ -3,6 +3,10 @@ module HpcUtils where
import Trace.Hpc.Util
import qualified Data.Map as Map
+dropWhileEndLE :: (a -> Bool) -> [a] -> [a]
+-- Spec: dropWhileEndLE p = reverse . dropWhileEnd . reverse
+dropWhileEndLE p = foldr (\x r -> if null r && p x then [] else x:r) []
+
-- turns \n into ' '
-- | grab's the text behind a HpcPos;
grabHpcPos :: Map.Map Int String -> HpcPos -> String
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