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 <andy@dcs.gla.ac.uk>
-- 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 -> c) -> (b -> a) -> b -> b -> c
on cmp sel = \x y -> sel x `cmp` sel y

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

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

count :: (a -> Bool) -> [a] -> Int
count _ [] = 0
count p (x:xs) | p x       = 1 + count p xs
               | otherwise = count p xs

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

-- drop from the end of a list
dropTail :: Int -> [a] -> [a]
dropTail n = reverse . drop n . reverse

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

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 }

removeSpaces :: String -> String
removeSpaces = reverse . dropWhile isSpace . reverse . dropWhile isSpace

-- | Find the "restricted" Damerau-Levenshtein edit distance between two strings. See: <http://en.wikipedia.org/wiki/Damerau-Levenshtein_distance>.
-- Based on the algorithm presented in "A Bit-Vector Algorithm for Computing Levenshtein and Damerau Edit Distances" in PSC'02 (Heikki Hyyro).
-- See http://www.cs.uta.fi/~helmu/pubs/psc02.pdf and http://www.cs.uta.fi/~helmu/pubs/PSCerr.html for an explanation
restrictedDamerauLevenshteinDistance :: String -> String -> Int
restrictedDamerauLevenshteinDistance str1 str2 = restrictedDamerauLevenshteinDistanceWithLengths m n str1 str2
  where
    m = length str1
    n = length str2

restrictedDamerauLevenshteinDistanceWithLengths :: Int -> Int -> String -> String -> Int
restrictedDamerauLevenshteinDistanceWithLengths m n str1 str2
  | m <= n    = if n <= 32 -- n must be larger so this check is sufficient
                then restrictedDamerauLevenshteinDistance' (undefined :: Word32) m n str1 str2
                else restrictedDamerauLevenshteinDistance' (undefined :: Integer) m n str1 str2
  | otherwise = if m <= 32 -- m must be larger so this check is sufficient
                then restrictedDamerauLevenshteinDistance' (undefined :: Word32) n m str2 str1
                else restrictedDamerauLevenshteinDistance' (undefined :: Integer) n m str2 str1

restrictedDamerauLevenshteinDistance' :: (Bits bv) => bv -> Int -> Int -> String -> String -> Int
restrictedDamerauLevenshteinDistance' _bv_dummy m n str1 str2 
  | [] <- str1 = n
  | otherwise  = extractAnswer $ foldl' (restrictedDamerauLevenshteinDistanceWorker (matchVectors str1) top_bit_mask vector_mask) (0, 0, m_ones, 0, m) str2
  where m_ones@vector_mask = (2 ^ m) - 1
        top_bit_mask = (1 `shiftL` (m - 1)) `asTypeOf` _bv_dummy
        extractAnswer (_, _, _, _, distance) = distance

restrictedDamerauLevenshteinDistanceWorker :: (Bits bv) => IM.IntMap bv -> bv -> bv -> (bv, bv, bv, bv, Int) -> Char -> (bv, bv, bv, bv, Int)
restrictedDamerauLevenshteinDistanceWorker str1_mvs top_bit_mask vector_mask (pm, d0, vp, vn, distance) char2 
  = seq str1_mvs $ seq top_bit_mask $ seq vector_mask $ seq pm' $ seq d0' $ seq vp' $ seq vn' $ seq distance'' $ seq char2 $ (pm', d0', vp', vn', distance'')
  where
    pm' = IM.findWithDefault 0 (ord char2) str1_mvs
    
    d0' = ((((sizedComplement vector_mask d0) .&. pm') `shiftL` 1) .&. pm) -- No need to mask the shiftL because of the restricted range of pm
      .|. ((((pm' .&. vp) + vp) .&. vector_mask) `xor` vp) .|. pm' .|. vn
    hp' = vn .|. sizedComplement vector_mask (d0' .|. vp)
    hn' = d0' .&. vp
    
    hp'_shift = ((hp' `shiftL` 1) .|. 1) .&. vector_mask
    hn'_shift = (hn' `shiftL` 1) .&. vector_mask
    vp' = hn'_shift .|. sizedComplement vector_mask (d0' .|. hp'_shift)
    vn' = d0' .&. hp'_shift
    
    distance' = if hp' .&. top_bit_mask /= 0 then distance + 1 else distance
    distance'' = if hn' .&. top_bit_mask /= 0 then distance' - 1 else distance'

sizedComplement :: Bits bv => bv -> bv -> bv
sizedComplement vector_mask vect = vector_mask `xor` vect

matchVectors :: Bits bv => String -> IM.IntMap bv
matchVectors = snd . foldl' go (0 :: Int, IM.empty)
  where
    go (ix, im) char = let ix' = ix + 1
                           im' = IM.insertWith (.|.) (ord char) (2 ^ ix) im
                       in seq ix' $ seq im' $ (ix', im')

#ifdef __GLASGOW_HASKELL__
{-# SPECIALIZE INLINE restrictedDamerauLevenshteinDistance' :: Word32 -> Int -> Int -> String -> String -> Int #-}
{-# SPECIALIZE INLINE restrictedDamerauLevenshteinDistance' :: Integer -> Int -> Int -> String -> String -> Int #-}

{-# SPECIALIZE restrictedDamerauLevenshteinDistanceWorker :: IM.IntMap Word32 -> Word32 -> Word32 -> (Word32, Word32, Word32, Word32, Int) -> Char -> (Word32, Word32, Word32, Word32, Int) #-}
{-# SPECIALIZE restrictedDamerauLevenshteinDistanceWorker :: IM.IntMap Integer -> Integer -> Integer -> (Integer, Integer, Integer, Integer, Int) -> Char -> (Integer, Integer, Integer, Integer, Int) #-}

{-# SPECIALIZE INLINE sizedComplement :: Word32 -> Word32 -> Word32 #-}
{-# SPECIALIZE INLINE sizedComplement :: Integer -> Integer -> Integer #-}

{-# SPECIALIZE matchVectors :: String -> IM.IntMap Word32 #-}
{-# SPECIALIZE matchVectors :: String -> IM.IntMap Integer #-}
#endif

-- | Search for possible matches to the users input in the given list, returning a small number of ranked results
fuzzyMatch :: String -> [String] -> [String]
fuzzyMatch user_entered possibilites = map fst $ take mAX_RESULTS $ sortBy (comparing snd) 
                                                [ (poss, distance) | poss <- possibilites
                                                                   , let distance = restrictedDamerauLevenshteinDistance poss user_entered
                                                                   , distance <= fuzzy_threshold ]
  where -- Work out an approriate match threshold (about a quarter of the # of characters the user entered)
        fuzzy_threshold = max (round $ fromInteger (genericLength user_entered) / (4 :: Rational)) 1
        mAX_RESULTS = 3

unzipWith :: (a -> b -> c) -> [(a, b)] -> [c]
unzipWith f pairs = map ( \ (a, b) -> f a b ) pairs

seqList :: [a] -> b -> b
seqList [] b = b
seqList (x:xs) b = x `seq` seqList xs b

global :: a -> IORef a
global a = unsafePerformIO (newIORef a)

consIORef :: IORef [a] -> a -> IO ()
consIORef var x = do
  atomicModifyIORef var (\xs -> (x:xs,()))

globalMVar :: a -> MVar a
globalMVar a = unsafePerformIO (newMVar a)

globalEmptyMVar :: MVar a
globalEmptyMVar = unsafePerformIO newEmptyMVar

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 == '_' || c == '\'') && go cs

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)

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 -> '\\'

abstractConstr :: String -> Constr
abstractConstr n = mkConstr (abstractDataType n) ("{abstract:"++n++"}") [] Prefix

abstractDataType :: String -> DataType
abstractDataType n = mkDataType n [abstractConstr n]

-- Old GHC versions come with a base library with this function misspelled.
#if __GLASGOW_HASKELL__ < 612
mkNoRepType :: String -> DataType
mkNoRepType = mkNorepType
#endif