%
% (c) The University of Glasgow 2006
% (c) The University of Glasgow 1992-2002
%
\begin{code}
-- | Highly random utility functions
module Util (
-- * Flags dependent on the compiler build
ghciSupported, debugIsOn, ghciTablesNextToCode, picIsOn,
isWindowsHost, isWindowsTarget, isDarwinTarget,
-- * General list processing
zipEqual, zipWithEqual, zipWith3Equal, zipWith4Equal,
zipLazy, stretchZipWith,
unzipWith,
mapFst, mapSnd,
mapAndUnzip, mapAndUnzip3,
nOfThem, filterOut, partitionWith, splitEithers,
foldl1', foldl2, count, all2,
lengthExceeds, lengthIs, lengthAtLeast,
listLengthCmp, atLength, equalLength, compareLength,
isSingleton, only, singleton,
notNull, snocView,
isIn, isn'tIn,
-- * List operations controlled by another list
takeList, dropList, splitAtList, split,
-- * For loop
nTimes,
-- * Sorting
sortLe, sortWith, on,
-- * Comparisons
isEqual, eqListBy,
thenCmp, cmpList, maybePrefixMatch,
removeSpaces,
-- * Transitive closures
transitiveClosure,
-- * Strictness
seqList,
-- * Module names
looksLikeModuleName,
-- * Argument processing
getCmd, toCmdArgs, toArgs,
-- * Floating point
readRational,
-- * IO-ish utilities
createDirectoryHierarchy,
doesDirNameExist,
modificationTimeIfExists,
global, consIORef,
-- * Filenames and paths
Suffix,
splitLongestPrefix,
escapeSpaces,
parseSearchPath,
Direction(..), reslash,
) where
#include "HsVersions.h"
import Panic
import Data.IORef ( IORef, newIORef )
import System.IO.Unsafe ( unsafePerformIO )
import Data.IORef ( readIORef, writeIORef )
import Data.List hiding (group)
import qualified Data.List as List ( elem )
#ifdef DEBUG
import qualified Data.List as List ( notElem )
import FastTypes
#endif
import Control.Monad ( unless )
import System.IO.Error as IO ( catch, isDoesNotExistError )
import System.Directory ( doesDirectoryExist, createDirectory,
getModificationTime )
import System.FilePath
import Data.Char ( isUpper, isAlphaNum, isSpace, ord, isDigit )
import Data.Ratio ( (%) )
import System.Time ( ClockTime )
infixr 9 `thenCmp`
\end{code}
%************************************************************************
%* *
\subsection{Is DEBUG on, are we on Windows, etc?}
%* *
%************************************************************************
These booleans are global constants, set by CPP flags. They allow us to
recompile a single module (this one) to change whether or not debug output
appears. They sometimes let us avoid even running CPP elsewhere.
It's important that the flags are literal constants (True/False). Then,
with -0, tests of the flags in other modules will simplify to the correct
branch of the conditional, thereby dropping debug code altogether when
the flags are off.
\begin{code}
ghciSupported :: Bool
#ifdef GHCI
ghciSupported = True
#else
ghciSupported = False
#endif
debugIsOn :: Bool
#ifdef DEBUG
debugIsOn = True
#else
debugIsOn = False
#endif
ghciTablesNextToCode :: Bool
#ifdef GHCI_TABLES_NEXT_TO_CODE
ghciTablesNextToCode = True
#else
ghciTablesNextToCode = False
#endif
picIsOn :: Bool
#ifdef __PIC__
picIsOn = True
#else
picIsOn = False
#endif
isWindowsHost :: Bool
#ifdef mingw32_HOST_OS
isWindowsHost = True
#else
isWindowsHost = False
#endif
isWindowsTarget :: Bool
#ifdef mingw32_TARGET_OS
isWindowsTarget = True
#else
isWindowsTarget = False
#endif
isDarwinTarget :: Bool
#ifdef darwin_TARGET_OS
isDarwinTarget = True
#else
isDarwinTarget = False
#endif
\end{code}
%************************************************************************
%* *
\subsection{A for loop}
%* *
%************************************************************************
\begin{code}
-- | Compose a function with itself n times. (nth rather than twice)
nTimes :: Int -> (a -> a) -> (a -> a)
nTimes 0 _ = id
nTimes 1 f = f
nTimes n f = f . nTimes (n-1) f
\end{code}
%************************************************************************
%* *
\subsection[Utils-lists]{General list processing}
%* *
%************************************************************************
\begin{code}
filterOut :: (a->Bool) -> [a] -> [a]
-- ^ Like filter, only it reverses the sense of the test
filterOut _ [] = []
filterOut p (x:xs) | p x = filterOut p xs
| otherwise = x : filterOut p xs
partitionWith :: (a -> Either b c) -> [a] -> ([b], [c])
-- ^ Uses a function to determine which of two output lists an input element should join
partitionWith _ [] = ([],[])
partitionWith f (x:xs) = case f x of
Left b -> (b:bs, cs)
Right c -> (bs, c:cs)
where (bs,cs) = partitionWith f xs
splitEithers :: [Either a b] -> ([a], [b])
-- ^ Teases a list of 'Either's apart into two lists
splitEithers [] = ([],[])
splitEithers (e : es) = case e of
Left x -> (x:xs, ys)
Right y -> (xs, y:ys)
where (xs,ys) = splitEithers es
\end{code}
A paranoid @zip@ (and some @zipWith@ friends) that checks the lists
are of equal length. Alastair Reid thinks this should only happen if
DEBUGging on; hey, why not?
\begin{code}
zipEqual :: String -> [a] -> [b] -> [(a,b)]
zipWithEqual :: String -> (a->b->c) -> [a]->[b]->[c]
zipWith3Equal :: String -> (a->b->c->d) -> [a]->[b]->[c]->[d]
zipWith4Equal :: String -> (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]
#ifndef DEBUG
zipEqual _ = zip
zipWithEqual _ = zipWith
zipWith3Equal _ = zipWith3
zipWith4Equal _ = zipWith4
#else
zipEqual _ [] [] = []
zipEqual msg (a:as) (b:bs) = (a,b) : zipEqual msg as bs
zipEqual msg _ _ = panic ("zipEqual: unequal lists:"++msg)
zipWithEqual msg z (a:as) (b:bs)= z a b : zipWithEqual msg z as bs
zipWithEqual _ _ [] [] = []
zipWithEqual msg _ _ _ = panic ("zipWithEqual: unequal lists:"++msg)
zipWith3Equal msg z (a:as) (b:bs) (c:cs)
= z a b c : zipWith3Equal msg z as bs cs
zipWith3Equal _ _ [] [] [] = []
zipWith3Equal msg _ _ _ _ = panic ("zipWith3Equal: unequal lists:"++msg)
zipWith4Equal msg z (a:as) (b:bs) (c:cs) (d:ds)
= z a b c d : zipWith4Equal msg z as bs cs ds
zipWith4Equal _ _ [] [] [] [] = []
zipWith4Equal msg _ _ _ _ _ = panic ("zipWith4Equal: unequal lists:"++msg)
#endif
\end{code}
\begin{code}
-- | 'zipLazy' is a kind of 'zip' that is lazy in the second list (observe the ~)
zipLazy :: [a] -> [b] -> [(a,b)]
zipLazy [] _ = []
-- We want to write this, but with GHC 6.4 we get a warning, so it
-- doesn't validate:
-- zipLazy (x:xs) ~(y:ys) = (x,y) : zipLazy xs ys
-- so we write this instead:
zipLazy (x:xs) zs = let y : ys = zs
in (x,y) : zipLazy xs ys
\end{code}
\begin{code}
stretchZipWith :: (a -> Bool) -> b -> (a->b->c) -> [a] -> [b] -> [c]
-- ^ @stretchZipWith p z f xs ys@ stretches @ys@ by inserting @z@ in
-- the places where @p@ returns @True@
stretchZipWith _ _ _ [] _ = []
stretchZipWith p z f (x:xs) ys
| p x = f x z : stretchZipWith p z f xs ys
| otherwise = case ys of
[] -> []
(y:ys) -> f x y : stretchZipWith p z f xs ys
\end{code}
\begin{code}
mapFst :: (a->c) -> [(a,b)] -> [(c,b)]
mapSnd :: (b->c) -> [(a,b)] -> [(a,c)]
mapFst f xys = [(f x, y) | (x,y) <- xys]
mapSnd f xys = [(x, f y) | (x,y) <- xys]
mapAndUnzip :: (a -> (b, c)) -> [a] -> ([b], [c])
mapAndUnzip _ [] = ([], [])
mapAndUnzip f (x:xs)
= let (r1, r2) = f x
(rs1, rs2) = mapAndUnzip f xs
in
(r1:rs1, r2:rs2)
mapAndUnzip3 :: (a -> (b, c, d)) -> [a] -> ([b], [c], [d])
mapAndUnzip3 _ [] = ([], [], [])
mapAndUnzip3 f (x:xs)
= let (r1, r2, r3) = f x
(rs1, rs2, rs3) = mapAndUnzip3 f xs
in
(r1:rs1, r2:rs2, r3:rs3)
\end{code}
\begin{code}
nOfThem :: Int -> a -> [a]
nOfThem n thing = replicate n thing
-- | @atLength atLen atEnd ls n@ unravels list @ls@ to position @n@. Precisely:
--
-- @
-- atLength atLenPred atEndPred ls n
-- | n < 0 = atLenPred n
-- | length ls < n = atEndPred (n - length ls)
-- | otherwise = atLenPred (drop n ls)
-- @
atLength :: ([a] -> b)
-> (Int -> b)
-> [a]
-> Int
-> b
atLength atLenPred atEndPred ls n
| n < 0 = atEndPred n
| otherwise = go n ls
where
go n [] = atEndPred n
go 0 ls = atLenPred ls
go n (_:xs) = go (n-1) xs
-- Some special cases of atLength:
lengthExceeds :: [a] -> Int -> Bool
-- ^ > (lengthExceeds xs n) = (length xs > n)
lengthExceeds = atLength notNull (const False)
lengthAtLeast :: [a] -> Int -> Bool
lengthAtLeast = atLength notNull (== 0)
lengthIs :: [a] -> Int -> Bool
lengthIs = atLength null (==0)
listLengthCmp :: [a] -> Int -> Ordering
listLengthCmp = atLength atLen atEnd
where
atEnd 0 = EQ
atEnd x
| x > 0 = LT -- not yet seen 'n' elts, so list length is < n.
| otherwise = GT
atLen [] = EQ
atLen _ = GT
equalLength :: [a] -> [b] -> Bool
equalLength [] [] = True
equalLength (_:xs) (_:ys) = equalLength xs ys
equalLength _ _ = False
compareLength :: [a] -> [b] -> Ordering
compareLength [] [] = EQ
compareLength (_:xs) (_:ys) = compareLength xs ys
compareLength [] _ = LT
compareLength _ [] = GT
----------------------------
singleton :: a -> [a]
singleton x = [x]
isSingleton :: [a] -> Bool
isSingleton [_] = True
isSingleton _ = False
notNull :: [a] -> Bool
notNull [] = False
notNull _ = True
only :: [a] -> a
#ifdef DEBUG
only [a] = a
#else
only (a:_) = a
#endif
only _ = panic "Util: only"
\end{code}
Debugging/specialising versions of \tr{elem} and \tr{notElem}
\begin{code}
isIn, isn'tIn :: Eq a => String -> a -> [a] -> Bool
# ifndef DEBUG
isIn _msg x ys = elem__ x ys
isn'tIn _msg x ys = notElem__ x ys
--these are here to be SPECIALIZEd (automagically)
elem__ :: Eq a => a -> [a] -> Bool
elem__ _ [] = False
elem__ x (y:ys) = x == y || elem__ x ys
notElem__ :: Eq a => a -> [a] -> Bool
notElem__ _ [] = True
notElem__ x (y:ys) = x /= y && notElem__ x ys
# else /* DEBUG */
isIn msg x ys
= elem (_ILIT(0)) x ys
where
elem _ _ [] = False
elem i x (y:ys)
| i ># _ILIT(100) = trace ("Over-long elem in " ++ msg)
(x `List.elem` (y:ys))
| otherwise = x == y || elem (i +# _ILIT(1)) x ys
isn'tIn msg x ys
= notElem (_ILIT(0)) x ys
where
notElem _ _ [] = True
notElem i x (y:ys)
| i ># _ILIT(100) = trace ("Over-long notElem in " ++ msg)
(x `List.notElem` (y:ys))
| otherwise = x /= y && notElem (i +# _ILIT(1)) x ys
# endif /* DEBUG */
\end{code}
%************************************************************************
%* *
\subsubsection[Utils-Carsten-mergesort]{A mergesort from Carsten}
%* *
%************************************************************************
\begin{display}
Date: Mon, 3 May 93 20:45:23 +0200
From: Carsten Kehler Holst
To: partain@dcs.gla.ac.uk
Subject: natural merge sort beats quick sort [ and it is prettier ]
Here is a piece of Haskell code that I'm rather fond of. See it as an
attempt to get rid of the ridiculous quick-sort routine. group is
quite useful by itself I think it was John's idea originally though I
believe the lazy version is due to me [surprisingly complicated].
gamma [used to be called] is called gamma because I got inspired by
the Gamma calculus. It is not very close to the calculus but does
behave less sequentially than both foldr and foldl. One could imagine
a version of gamma that took a unit element as well thereby avoiding
the problem with empty lists.
I've tried this code against
1) insertion sort - as provided by haskell
2) the normal implementation of quick sort
3) a deforested version of quick sort due to Jan Sparud
4) a super-optimized-quick-sort of Lennart's
If the list is partially sorted both merge sort and in particular
natural merge sort wins. If the list is random [ average length of
rising subsequences = approx 2 ] mergesort still wins and natural
merge sort is marginally beaten by Lennart's soqs. The space
consumption of merge sort is a bit worse than Lennart's quick sort
approx a factor of 2. And a lot worse if Sparud's bug-fix [see his
fpca article ] isn't used because of group.
have fun
Carsten
\end{display}
\begin{code}
group :: (a -> a -> Bool) -> [a] -> [[a]]
-- Given a <= function, group finds maximal contiguous up-runs
-- or down-runs in the input list.
-- It's stable, in the sense that it never re-orders equal elements
--
-- Date: Mon, 12 Feb 1996 15:09:41 +0000
-- From: Andy Gill
-- Here is a `better' definition of group.
group _ [] = []
group p (x:xs) = group' xs x x (x :)
where
group' [] _ _ s = [s []]
group' (x:xs) x_min x_max s
| x_max `p` x = group' xs x_min x (s . (x :))
| not (x_min `p` x) = group' xs x x_max ((x :) . s)
| otherwise = s [] : group' xs x x (x :)
-- NB: the 'not' is essential for stablity
-- x `p` x_min would reverse equal elements
generalMerge :: (a -> a -> Bool) -> [a] -> [a] -> [a]
generalMerge _ xs [] = xs
generalMerge _ [] ys = ys
generalMerge p (x:xs) (y:ys) | x `p` y = x : generalMerge p xs (y:ys)
| otherwise = y : generalMerge p (x:xs) ys
-- gamma is now called balancedFold
balancedFold :: (a -> a -> a) -> [a] -> a
balancedFold _ [] = error "can't reduce an empty list using balancedFold"
balancedFold _ [x] = x
balancedFold f l = balancedFold f (balancedFold' f l)
balancedFold' :: (a -> a -> a) -> [a] -> [a]
balancedFold' f (x:y:xs) = f x y : balancedFold' f xs
balancedFold' _ xs = xs
generalNaturalMergeSort :: (a -> a -> Bool) -> [a] -> [a]
generalNaturalMergeSort _ [] = []
generalNaturalMergeSort p xs = (balancedFold (generalMerge p) . group p) xs
#if NOT_USED
generalMergeSort p [] = []
generalMergeSort p xs = (balancedFold (generalMerge p) . map (: [])) xs
mergeSort, naturalMergeSort :: Ord a => [a] -> [a]
mergeSort = generalMergeSort (<=)
naturalMergeSort = generalNaturalMergeSort (<=)
mergeSortLe le = generalMergeSort le
#endif
sortLe :: (a->a->Bool) -> [a] -> [a]
sortLe le = generalNaturalMergeSort le
sortWith :: Ord b => (a->b) -> [a] -> [a]
sortWith get_key xs = sortLe le xs
where
x `le` y = get_key x < get_key y
on :: (a -> a -> Ordering) -> (b -> a) -> b -> b -> Ordering
on cmp sel = \x y -> sel x `cmp` sel y
\end{code}
%************************************************************************
%* *
\subsection[Utils-transitive-closure]{Transitive closure}
%* *
%************************************************************************
This algorithm for transitive closure is straightforward, albeit quadratic.
\begin{code}
transitiveClosure :: (a -> [a]) -- Successor function
-> (a -> a -> Bool) -- Equality predicate
-> [a]
-> [a] -- The transitive closure
transitiveClosure succ eq xs
= go [] xs
where
go done [] = done
go done (x:xs) | x `is_in` done = go done xs
| otherwise = go (x:done) (succ x ++ xs)
_ `is_in` [] = False
x `is_in` (y:ys) | eq x y = True
| otherwise = x `is_in` ys
\end{code}
%************************************************************************
%* *
\subsection[Utils-accum]{Accumulating}
%* *
%************************************************************************
A combination of foldl with zip. It works with equal length lists.
\begin{code}
foldl2 :: (acc -> a -> b -> acc) -> acc -> [a] -> [b] -> acc
foldl2 _ z [] [] = z
foldl2 k z (a:as) (b:bs) = foldl2 k (k z a b) as bs
foldl2 _ _ _ _ = panic "Util: foldl2"
all2 :: (a -> b -> Bool) -> [a] -> [b] -> Bool
-- True if the lists are the same length, and
-- all corresponding elements satisfy the predicate
all2 _ [] [] = True
all2 p (x:xs) (y:ys) = p x y && all2 p xs ys
all2 _ _ _ = False
\end{code}
Count the number of times a predicate is true
\begin{code}
count :: (a -> Bool) -> [a] -> Int
count _ [] = 0
count p (x:xs) | p x = 1 + count p xs
| otherwise = count p xs
\end{code}
@splitAt@, @take@, and @drop@ but with length of another
list giving the break-off point:
\begin{code}
takeList :: [b] -> [a] -> [a]
takeList [] _ = []
takeList (_:xs) ls =
case ls of
[] -> []
(y:ys) -> y : takeList xs ys
dropList :: [b] -> [a] -> [a]
dropList [] xs = xs
dropList _ xs@[] = xs
dropList (_:xs) (_:ys) = dropList xs ys
splitAtList :: [b] -> [a] -> ([a], [a])
splitAtList [] xs = ([], xs)
splitAtList _ xs@[] = (xs, xs)
splitAtList (_:xs) (y:ys) = (y:ys', ys'')
where
(ys', ys'') = splitAtList xs ys
snocView :: [a] -> Maybe ([a],a)
-- Split off the last element
snocView [] = Nothing
snocView xs = go [] xs
where
-- Invariant: second arg is non-empty
go acc [x] = Just (reverse acc, x)
go acc (x:xs) = go (x:acc) xs
go _ [] = panic "Util: snocView"
split :: Char -> String -> [String]
split c s = case rest of
[] -> [chunk]
_:rest -> chunk : split c rest
where (chunk, rest) = break (==c) s
\end{code}
%************************************************************************
%* *
\subsection[Utils-comparison]{Comparisons}
%* *
%************************************************************************
\begin{code}
isEqual :: Ordering -> Bool
-- Often used in (isEqual (a `compare` b))
isEqual GT = False
isEqual EQ = True
isEqual LT = False
thenCmp :: Ordering -> Ordering -> Ordering
{-# INLINE thenCmp #-}
thenCmp EQ ordering = ordering
thenCmp ordering _ = ordering
eqListBy :: (a->a->Bool) -> [a] -> [a] -> Bool
eqListBy _ [] [] = True
eqListBy eq (x:xs) (y:ys) = eq x y && eqListBy eq xs ys
eqListBy _ _ _ = False
cmpList :: (a -> a -> Ordering) -> [a] -> [a] -> Ordering
-- `cmpList' uses a user-specified comparer
cmpList _ [] [] = EQ
cmpList _ [] _ = LT
cmpList _ _ [] = GT
cmpList cmp (a:as) (b:bs)
= case cmp a b of { EQ -> cmpList cmp as bs; xxx -> xxx }
\end{code}
\begin{code}
-- This (with a more general type) is Data.List.stripPrefix from GHC 6.8.
-- This definition can be removed once we require at least 6.8 to build.
maybePrefixMatch :: String -> String -> Maybe String
maybePrefixMatch [] rest = Just rest
maybePrefixMatch (_:_) [] = Nothing
maybePrefixMatch (p:pat) (r:rest)
| p == r = maybePrefixMatch pat rest
| otherwise = Nothing
removeSpaces :: String -> String
removeSpaces = reverse . dropWhile isSpace . reverse . dropWhile isSpace
\end{code}
%************************************************************************
%* *
\subsection[Utils-pairs]{Pairs}
%* *
%************************************************************************
\begin{code}
unzipWith :: (a -> b -> c) -> [(a, b)] -> [c]
unzipWith f pairs = map ( \ (a, b) -> f a b ) pairs
\end{code}
\begin{code}
seqList :: [a] -> b -> b
seqList [] b = b
seqList (x:xs) b = x `seq` seqList xs b
\end{code}
Global variables:
\begin{code}
global :: a -> IORef a
global a = unsafePerformIO (newIORef a)
\end{code}
\begin{code}
consIORef :: IORef [a] -> a -> IO ()
consIORef var x = do
xs <- readIORef var
writeIORef var (x:xs)
\end{code}
Module names:
\begin{code}
looksLikeModuleName :: String -> Bool
looksLikeModuleName [] = False
looksLikeModuleName (c:cs) = isUpper c && go cs
where go [] = True
go ('.':cs) = looksLikeModuleName cs
go (c:cs) = (isAlphaNum c || c == '_') && go cs
\end{code}
Akin to @Prelude.words@, but acts like the Bourne shell, treating
quoted strings as Haskell Strings, and also parses Haskell [String]
syntax.
\begin{code}
getCmd :: String -> Either String -- Error
(String, String) -- (Cmd, Rest)
getCmd s = case break isSpace $ dropWhile isSpace s of
([], _) -> Left ("Couldn't find command in " ++ show s)
res -> Right res
toCmdArgs :: String -> Either String -- Error
(String, [String]) -- (Cmd, Args)
toCmdArgs s = case getCmd s of
Left err -> Left err
Right (cmd, s') -> case toArgs s' of
Left err -> Left err
Right args -> Right (cmd, args)
toArgs :: String -> Either String -- Error
[String] -- Args
toArgs str
= case dropWhile isSpace str of
s@('[':_) -> case reads s of
[(args, spaces)]
| all isSpace spaces ->
Right args
_ ->
Left ("Couldn't read " ++ show str ++ "as [String]")
s -> toArgs' s
where
toArgs' s = case dropWhile isSpace s of
[] -> Right []
('"' : _) -> case reads s of
[(arg, rest)]
-- rest must either be [] or start with a space
| all isSpace (take 1 rest) ->
case toArgs' rest of
Left err -> Left err
Right args -> Right (arg : args)
_ ->
Left ("Couldn't read " ++ show s ++ "as String")
s' -> case break isSpace s' of
(arg, s'') -> case toArgs' s'' of
Left err -> Left err
Right args -> Right (arg : args)
\end{code}
-- -----------------------------------------------------------------------------
-- Floats
\begin{code}
readRational__ :: ReadS Rational -- NB: doesn't handle leading "-"
readRational__ r = do
(n,d,s) <- readFix r
(k,t) <- readExp s
return ((n%1)*10^^(k-d), t)
where
readFix r = do
(ds,s) <- lexDecDigits r
(ds',t) <- lexDotDigits s
return (read (ds++ds'), length ds', t)
readExp (e:s) | e `elem` "eE" = readExp' s
readExp s = return (0,s)
readExp' ('+':s) = readDec s
readExp' ('-':s) = do (k,t) <- readDec s
return (-k,t)
readExp' s = readDec s
readDec s = do
(ds,r) <- nonnull isDigit s
return (foldl1 (\n d -> n * 10 + d) [ ord d - ord '0' | d <- ds ],
r)
lexDecDigits = nonnull isDigit
lexDotDigits ('.':s) = return (span isDigit s)
lexDotDigits s = return ("",s)
nonnull p s = do (cs@(_:_),t) <- return (span p s)
return (cs,t)
readRational :: String -> Rational -- NB: *does* handle a leading "-"
readRational top_s
= case top_s of
'-' : xs -> - (read_me xs)
xs -> read_me xs
where
read_me s
= case (do { (x,"") <- readRational__ s ; return x }) of
[x] -> x
[] -> error ("readRational: no parse:" ++ top_s)
_ -> error ("readRational: ambiguous parse:" ++ top_s)
-----------------------------------------------------------------------------
-- Create a hierarchy of directories
createDirectoryHierarchy :: FilePath -> IO ()
createDirectoryHierarchy dir | isDrive dir = return () -- XXX Hack
createDirectoryHierarchy dir = do
b <- doesDirectoryExist dir
unless b $ do createDirectoryHierarchy (takeDirectory dir)
createDirectory dir
-----------------------------------------------------------------------------
-- Verify that the 'dirname' portion of a FilePath exists.
--
doesDirNameExist :: FilePath -> IO Bool
doesDirNameExist fpath = case takeDirectory fpath of
"" -> return True -- XXX Hack
_ -> doesDirectoryExist (takeDirectory fpath)
-- --------------------------------------------------------------
-- check existence & modification time at the same time
modificationTimeIfExists :: FilePath -> IO (Maybe ClockTime)
modificationTimeIfExists f = do
(do t <- getModificationTime f; return (Just t))
`IO.catch` \e -> if isDoesNotExistError e
then return Nothing
else ioError e
-- split a string at the last character where 'pred' is True,
-- returning a pair of strings. The first component holds the string
-- up (but not including) the last character for which 'pred' returned
-- True, the second whatever comes after (but also not including the
-- last character).
--
-- If 'pred' returns False for all characters in the string, the original
-- string is returned in the first component (and the second one is just
-- empty).
splitLongestPrefix :: String -> (Char -> Bool) -> (String,String)
splitLongestPrefix str pred
| null r_pre = (str, [])
| otherwise = (reverse (tail r_pre), reverse r_suf)
-- 'tail' drops the char satisfying 'pred'
where (r_suf, r_pre) = break pred (reverse str)
escapeSpaces :: String -> String
escapeSpaces = foldr (\c s -> if isSpace c then '\\':c:s else c:s) ""
type Suffix = String
--------------------------------------------------------------
-- * Search path
--------------------------------------------------------------
-- | The function splits the given string to substrings
-- using the 'searchPathSeparator'.
parseSearchPath :: String -> [FilePath]
parseSearchPath path = split path
where
split :: String -> [String]
split s =
case rest' of
[] -> [chunk]
_:rest -> chunk : split rest
where
chunk =
case chunk' of
#ifdef mingw32_HOST_OS
('\"':xs@(_:_)) | last xs == '\"' -> init xs
#endif
_ -> chunk'
(chunk', rest') = break isSearchPathSeparator s
data Direction = Forwards | Backwards
reslash :: Direction -> FilePath -> FilePath
reslash d = f
where f ('/' : xs) = slash : f xs
f ('\\' : xs) = slash : f xs
f (x : xs) = x : f xs
f "" = ""
slash = case d of
Forwards -> '/'
Backwards -> '\\'
\end{code}