-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/
-- | Extra functions I use.
--
-- A library of extra functions for the standard Haskell libraries. Most
-- functions are simple additions, filling out missing functionality. A
-- few functions are available in later versions of GHC, but this package
-- makes them available back to GHC 7.2.
--
-- The module Extra documents all functions provided by this
-- library. Modules such as Data.List.Extra provide extra
-- functions over Data.List and also reexport Data.List.
-- Users are recommended to replace Data.List imports with
-- Data.List.Extra if they need the extra functionality.
@package extra
@version 0.5.1
-- | Extra functions for the current system info.
module System.Info.Extra
-- | Return True on Windows and False otherwise. A runtime
-- version of #ifdef minw32_HOST_OS. Equivalent to os ==
-- "mingw32", but: more efficient; doesn't require typing an easily
-- mistypeable string; actually asks about your OS not a library; doesn't
-- bake in 32bit assumptions that are already false. </rant>
--
--
-- isWindows == (os == "mingw32")
--
isWindows :: Bool
-- | Extra functions for System.Environment. All these functions are
-- available in later GHC versions, but this code works all the way back
-- to GHC 7.2.
module System.Environment.Extra
-- | Returns the absolute pathname of the current executable.
--
-- Note that for scripts and interactive sessions, this is the path to
-- the interpreter (e.g. ghci.)
getExecutablePath :: IO FilePath
-- | Return the value of the environment variable var, or
-- Nothing if there is no such value.
--
-- For POSIX users, this is equivalent to getEnv.
lookupEnv :: String -> IO (Maybe String)
-- | Extra numeric functions - formatting and specialised conversions.
module Numeric.Extra
-- | Show a number to a fixed number of decimal places.
--
--
-- showDP 4 pi == "3.1416"
-- showDP 0 pi == "3"
-- showDP 2 3 == "3.00"
--
showDP :: RealFloat a => Int -> a -> String
-- | Specialised numeric conversion, type restricted version of
-- fromIntegral.
intToDouble :: Int -> Double
-- | Specialised numeric conversion, type restricted version of
-- fromIntegral.
intToFloat :: Int -> Float
-- | Specialised numeric conversion, type restricted version of
-- realToFrac.
floatToDouble :: Float -> Double
-- | Specialised numeric conversion, type restricted version of
-- realToFrac.
doubleToFloat :: Double -> Float
-- | Extra functions for working with times. Unlike the other modules in
-- this package, there is no corresponding System.Time module.
-- This module enhances the functionality from Data.Time.Clock,
-- but in quite different ways.
--
-- Throughout, time is measured in Seconds, which is a type alias
-- for Double.
module System.Time.Extra
-- | A type alias for seconds, which are stored as Double.
type Seconds = Double
-- | Sleep for a number of seconds.
--
--
-- fmap (round . fst) (duration $ sleep 1) == return 1
--
sleep :: Seconds -> IO ()
-- | Calculate the difference between two times in seconds. Usually the
-- first time will be the end of an event, and the second time will be
-- the beginning.
--
--
-- \a b -> a > b ==> subtractTime a b > 0
--
subtractTime :: UTCTime -> UTCTime -> Seconds
-- | Show a number of seconds, typically a duration, in a suitable manner
-- with responable precision for a human.
--
--
-- showDuration 3.435 == "3.44s"
-- showDuration 623.8 == "10m24s"
-- showDuration 62003.8 == "17h13m"
-- showDuration 1e8 == "27777h47m"
--
showDuration :: Seconds -> String
-- | Call once to start, then call repeatedly to get the elapsed time since
-- the first call. Values will usually increase, unless the system clock
-- is updated (if you need the guarantee, see offsetTimeIncrease).
offsetTime :: IO (IO Seconds)
-- | Like offsetTime, but results will never decrease (though they
-- may stay the same).
--
--
-- do f <- offsetTimeIncrease; xs <- replicateM 10 f; return $ xs == sort xs
--
offsetTimeIncrease :: IO (IO Seconds)
-- | Record how long a computation takes in Seconds.
duration :: IO a -> IO (Seconds, a)
-- | Extra functions for working with pairs and triples. Some of these
-- functions are available in the Control.Arrow module, but here
-- are available specialised to pairs. Some operations work on triples.
module Data.Tuple.Extra
-- | Update the first component of a pair.
--
--
-- first succ (1,"test") == (2,"test")
--
first :: (a -> a') -> (a, b) -> (a', b)
-- | Update the second component of a pair.
--
--
-- second reverse (1,"test") == (1,"tset")
--
second :: (b -> b') -> (a, b) -> (a, b')
-- | Given two functions, apply one to the first component and one to the
-- second. A specialised version of ***.
--
--
-- (succ *** reverse) (1,"test") == (2,"tset")
--
(***) :: (a -> a') -> (b -> b') -> (a, b) -> (a', b')
-- | Given two functions, apply both to a single argument to form a pair. A
-- specialised version of &&&.
--
--
-- (succ &&& pred) 1 == (2,0)
--
(&&&) :: (a -> b) -> (a -> c) -> a -> (b, c)
-- | Duplicate a single value into a pair.
--
--
-- dupe 12 == (12, 12)
--
dupe :: a -> (a, a)
-- | Apply a single function to both components of a pair.
--
--
-- both succ (1,2) == (2,3)
--
both :: (a -> b) -> (a, a) -> (b, b)
-- | Extract the fst of a triple.
fst3 :: (a, b, c) -> a
-- | Extract the snd of a triple.
snd3 :: (a, b, c) -> b
-- | Extract the final element of a triple.
thd3 :: (a, b, c) -> c
-- | This module extends Data.List with extra functions of a similar
-- nature. The package also exports the existing Data.List
-- functions. Some of the names and semantics were inspired by the
-- text package.
module Data.List.Extra
-- | Convert a string to lower case.
--
--
-- lower "This is A TEST" == "this is a test"
-- lower "" == ""
--
lower :: String -> String
-- | Convert a string to upper case.
--
--
-- upper "This is A TEST" == "THIS IS A TEST"
-- upper "" == ""
--
upper :: String -> String
-- | Remove spaces from either side of a string. A combination of
-- trimEnd and trimStart.
--
--
-- trim " hello " == "hello"
-- trimStart " hello " == "hello "
-- trimEnd " hello " == " hello"
-- \s -> trim s == trimEnd (trimStart s)
--
trim :: String -> String
-- | Remove spaces from the start of a string, see trim.
trimStart :: String -> String
-- | Remove spaces from the end of a string, see trim.
trimEnd :: String -> String
-- | Split the first word off a string. Useful for when starting to parse
-- the beginning of a string, but you want to accurately perserve
-- whitespace in the rest of the string.
--
--
-- word1 "" == ("", "")
-- word1 "keyword rest of string" == ("keyword","rest of string")
-- word1 " keyword\n rest of string" == ("keyword","rest of string")
-- \s -> fst (word1 s) == concat (take 1 $ words s)
-- \s -> words (snd $ word1 s) == drop 1 (words s)
--
word1 :: String -> (String, String)
-- | Drop a number of elements from the end of the list.
--
--
-- dropEnd 3 "hello" == "he"
-- dropEnd 5 "bye" == ""
-- dropEnd (-1) "bye" == "bye"
-- \i xs -> dropEnd i xs `isPrefixOf` xs
-- \i xs -> length (dropEnd i xs) == max 0 (length xs - max 0 i)
-- \i -> take 3 (dropEnd 5 [i..]) == take 3 [i..]
--
dropEnd :: Int -> [a] -> [a]
-- | Take a number of elements from the end of the list.
--
--
-- takeEnd 3 "hello" == "llo"
-- takeEnd 5 "bye" == "bye"
-- takeEnd (-1) "bye" == ""
-- \i xs -> takeEnd i xs `isSuffixOf` xs
-- \i xs -> length (takeEnd i xs) == min (max 0 i) (length xs)
--
takeEnd :: Int -> [a] -> [a]
-- | Break, but from the end.
--
--
-- breakEnd isLower "youRE" == ("you","RE")
-- breakEnd isLower "youre" == ("youre","")
-- breakEnd isLower "YOURE" == ("","YOURE")
--
breakEnd :: (a -> Bool) -> [a] -> ([a], [a])
-- | Span, but from the end.
--
--
-- spanEnd isUpper "youRE" == ("you","RE")
-- spanEnd (not . isSpace) "x y z" == ("x y ","z")
-- \f xs-> spanEnd f xs == swap (both reverse (span f (reverse xs)))
--
spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
-- | The dropWhileEnd function drops the largest suffix of a list in
-- which the given predicate holds for all elements. For example:
--
--
-- dropWhileEnd isSpace "foo\n" == "foo"
-- dropWhileEnd isSpace "foo bar" == "foo bar"
-- dropWhileEnd isSpace ("foo\n" ++ undefined) == "foo" ++ undefined
--
dropWhileEnd :: (a -> Bool) -> [a] -> [a]
-- | A version of dropWhileEnd but with different strictness
-- properties. The function dropWhileEnd can be used on an
-- infinite list and tests the property on each character. In contrast,
-- dropWhileEnd' is strict in the spine of the list but only tests
-- the trailing suffix. This version usually outperforms
-- dropWhileEnd if the list is short or the test is expensive.
-- Note the tests below cover both the prime and non-prime variants.
--
--
-- dropWhileEnd isSpace "ab cde " == "ab cde"
-- dropWhileEnd' isSpace "ab cde " == "ab cde"
-- last (dropWhileEnd even [undefined,3]) == undefined
-- last (dropWhileEnd' even [undefined,3]) == 3
-- head (dropWhileEnd even (3:undefined)) == 3
-- head (dropWhileEnd' even (3:undefined)) == undefined
--
dropWhileEnd' :: (a -> Bool) -> [a] -> [a]
-- | A version of takeWhile operating from the end.
--
--
-- takeWhileEnd even [2,3,4,6] == [4,6]
--
takeWhileEnd :: (a -> Bool) -> [a] -> [a]
-- | Return the prefix of the second string if its suffix matches the
-- entire first string.
--
-- Examples:
--
--
-- stripSuffix "bar" "foobar" == Just "foo"
-- stripSuffix "" "baz" == Just "baz"
-- stripSuffix "foo" "quux" == Nothing
--
stripSuffix :: Eq a => [a] -> [a] -> Maybe [a]
-- | A variant of words with a custom test. In particular, adjacent
-- separators are discarded, as are leading or trailing separators.
--
--
-- wordsBy (== ':') "::xyz:abc::123::" == ["xyz","abc","123"]
-- \s -> wordsBy isSpace s == words s
--
wordsBy :: (a -> Bool) -> [a] -> [[a]]
-- | A variant of lines with a custom test. In particular, if there
-- is a trailing separator it will be discarded.
--
--
-- linesBy (== ':') "::xyz:abc::123::" == ["","","xyz","abc","","123",""]
-- \s -> linesBy (== '\n') s == lines s
-- linesBy (== ';') "my;list;here;" == ["my","list","here"]
--
linesBy :: (a -> Bool) -> [a] -> [[a]]
-- | Find the first instance of needle in haystack. The
-- first element of the returned tuple is the prefix of haystack
-- before needle is matched. The second is the remainder of
-- haystack, starting with the match.
--
--
-- breakOn "::" "a::b::c" == ("a", "::b::c")
-- breakOn "/" "foobar" == ("foobar", "")
-- \needle haystack -> let (prefix,match) = breakOn needle haystack in prefix ++ match == haystack
--
breakOn :: Eq a => [a] -> [a] -> ([a], [a])
-- | Similar to breakOn, but searches from the end of the string.
--
-- The first element of the returned tuple is the prefix of
-- haystack up to and including the last match of
-- needle. The second is the remainder of haystack,
-- following the match.
--
--
-- breakOnEnd "::" "a::b::c" == ("a::b::", "c")
--
breakOnEnd :: Eq a => [a] -> [a] -> ([a], [a])
-- | Break a list into pieces separated by the first list argument,
-- consuming the delimiter. An empty delimiter is invalid, and will cause
-- an error to be raised.
--
--
-- splitOn "\r\n" "a\r\nb\r\nd\r\ne" == ["a","b","d","e"]
-- splitOn "aaa" "aaaXaaaXaaaXaaa" == ["","X","X","X",""]
-- splitOn "x" "x" == ["",""]
-- splitOn "x" "" == [""]
-- \s x -> s /= "" ==> intercalate s (splitOn s x) == x
-- \c x -> splitOn [c] x == split (==c) x
--
splitOn :: Eq a => [a] -> [a] -> [[a]]
-- | Splits a list into components delimited by separators, where the
-- predicate returns True for a separator element. The resulting
-- components do not contain the separators. Two adjacent separators
-- result in an empty component in the output.
--
--
-- split (== 'a') "aabbaca" == ["","","bb","c",""]
-- split (== 'a') "" == [""]
-- split (== ':') "::xyz:abc::123::" == ["","","xyz","abc","","123","",""]
-- split (== ',') "my,list,here" == ["my","list","here"]
--
split :: (a -> Bool) -> [a] -> [[a]]
-- | Split a list into chunks of a given size. The last chunk may contain
-- fewer than n elements. The chunk size must be positive.
--
--
-- chunksOf 3 "my test" == ["my ","tes","t"]
-- chunksOf 3 "mytest" == ["myt","est"]
-- chunksOf 8 "" == []
-- chunksOf 0 "test" == undefined
--
chunksOf :: Int -> [a] -> [[a]]
-- | Non-recursive transform over a list, like maybe.
--
--
-- list 1 (\v _ -> v - 2) [5,6,7] == 3
-- list 1 (\v _ -> v - 2) [] == 1
-- \nil cons xs -> maybe nil (uncurry cons) (uncons xs) == list nil cons xs
--
list :: b -> (a -> [a] -> b) -> [a] -> b
-- | If the list is empty returns Nothing, otherwise returns the
-- head and the tail.
--
--
-- uncons "test" == Just ('t',"est")
-- uncons "" == Nothing
-- \xs -> uncons xs == if null xs then Nothing else Just (head xs, tail xs)
--
uncons :: [a] -> Maybe (a, [a])
-- | If the list is empty returns Nothing, otherwise returns the
-- init and the last.
--
--
-- unsnoc "test" == Just ("tes",'t')
-- unsnoc "" == Nothing
-- \xs -> unsnoc xs == if null xs then Nothing else Just (init xs, last xs)
--
unsnoc :: [a] -> Maybe ([a], a)
-- | Append an element to the start of a list, an alias for '(:)'.
--
--
-- cons 't' "est" == "test"
-- \x xs -> uncons (cons x xs) == Just (x,xs)
--
cons :: a -> [a] -> [a]
-- | Append an element to the end of a list, takes O(n) time.
--
--
-- snoc "tes" 't' == "test"
-- \xs x -> unsnoc (snoc xs x) == Just (xs,x)
--
snoc :: [a] -> a -> [a]
-- | Equivalent to drop 1, but likely to be faster and a single
-- lexeme.
--
--
-- drop1 "" == ""
-- drop1 "test" == "est"
-- \xs -> drop 1 xs == drop1 xs
--
drop1 :: [a] -> [a]
-- | A combination of group and sort.
--
--
-- groupSort [(1,'t'),(3,'t'),(2,'e'),(2,'s')] == [(1,"t"),(2,"es"),(3,"t")]
-- \xs -> map fst (groupSort xs) == sort (nub (map fst xs))
-- \xs -> concatMap snd (groupSort xs) == map snd (sortOn fst xs)
--
groupSort :: Ord k => [(k, v)] -> [(k, [v])]
-- | A version of nub where the equality is done on some extracted
-- value. nubOn f is equivalent to nubBy ((==) on
-- f), but has the performance advantage of only evaluating
-- f once for each element in the input list.
nubOn :: Eq b => (a -> b) -> [a] -> [a]
-- | A version of group where the equality is done on some extracted
-- value.
groupOn :: Eq b => (a -> b) -> [a] -> [[a]]
-- | Sort a list by comparing the results of a key function applied to each
-- element. sortOn f is equivalent to sortBy (comparing
-- f), but has the performance advantage of only evaluating
-- f once for each element in the input list. This is called the
-- decorate-sort-undecorate paradigm, or Schwartzian transform.
--
--
-- sortOn fst [(3,"z"),(1,""),(3,"a")] == [(1,""),(3,"z"),(3,"a")]
--
sortOn :: Ord b => (a -> b) -> [a] -> [a]
-- | Are two lists disjoint, with no elements in common.
--
--
-- disjoint [1,2,3] [4,5] == True
-- disjoint [1,2,3] [4,1] == False
--
disjoint :: Eq a => [a] -> [a] -> Bool
-- | Are all elements the same.
--
--
-- allSame [1,1,2] == False
-- allSame [1,1,1] == True
-- allSame [1] == True
-- allSame [] == True
-- allSame (1:1:2:undefined) == False
-- \xs -> allSame xs == (length (nub xs) <= 1)
--
allSame :: Eq a => [a] -> Bool
-- | Is there any element which occurs more than once.
--
--
-- anySame [1,1,2] == True
-- anySame [1,2,3] == False
-- anySame (1:2:1:undefined) == True
-- anySame [] == False
-- \xs -> anySame xs == (length (nub xs) < length xs)
--
anySame :: Eq a => [a] -> Bool
-- | Apply some operation repeatedly, producing an element of output and
-- the remainder of the list.
--
--
-- \xs -> repeatedly (splitAt 3) xs == chunksOf 3 xs
-- \xs -> repeatedly word1 (trim xs) == words xs
--
repeatedly :: ([a] -> (b, [a])) -> [a] -> [b]
-- | Flipped version of map.
--
--
-- for [1,2,3] (+1) == [2,3,4]
--
for :: [a] -> (a -> b) -> [b]
-- | Find the first element of a list for which the operation returns
-- Just, along with the result of the operation. Like find
-- but useful where the function also computes some expensive information
-- that can be reused. Particular useful when the function is monadic,
-- see firstJustM.
--
--
-- firstJust id [Nothing,Just 3] == Just 3
-- firstJust id [Nothing,Nothing] == Nothing
--
firstJust :: (a -> Maybe b) -> [a] -> Maybe b
-- | A merging of unzip and concat.
--
--
-- concatUnzip [("a","AB"),("bc","C")] == ("abc","ABC")
--
concatUnzip :: [([a], [b])] -> ([a], [b])
-- | A merging of unzip3 and concat.
--
--
-- concatUnzip3 [("a","AB",""),("bc","C","123")] == ("abc","ABC","123")
--
concatUnzip3 :: [([a], [b], [c])] -> ([a], [b], [c])
-- | Replace a subsequence everywhere it occurs. The first argument must
-- not be the empty list.
--
--
-- replace "el" "_" "Hello Bella" == "H_lo B_la"
-- replace "el" "e" "Hello" == "Helo"
-- replace "" "e" "Hello" == undefined
-- \xs ys -> not (null xs) ==> replace xs xs ys == ys
--
replace :: Eq a => [a] -> [a] -> [a] -> [a]
-- | Merge two lists which are assumed to be ordered.
--
--
-- merge "ace" "bd" == "abcde"
-- \xs ys -> merge (sort xs) (sort ys) == sort (xs ++ ys)
--
merge :: Ord a => [a] -> [a] -> [a]
-- | Like merge, but with a custom ordering function.
mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
module Data.IORef.Extra
-- | Strict version of modifyIORef
modifyIORef' :: IORef a -> (a -> a) -> IO ()
-- | Evaluates the value before calling writeIORef.
writeIORef' :: IORef a -> a -> IO ()
-- | Strict version of atomicModifyIORef. This forces both the value
-- stored in the IORef as well as the value returned.
atomicModifyIORef' :: IORef a -> (a -> (a, b)) -> IO b
-- | Variant of writeIORef with the "barrier to reordering" property
-- that atomicModifyIORef has.
atomicWriteIORef :: IORef a -> a -> IO ()
-- | Evaluates the value before calling atomicWriteIORef.
atomicWriteIORef' :: IORef a -> a -> IO ()
module Data.Either.Extra
-- | Test if an Either value is the Left constructor.
-- Provided as standard with GHC 7.8 and above.
isLeft :: Either l r -> Bool
-- | Test if an Either value is the Right constructor.
-- Provided as standard with GHC 7.8 and above.
isRight :: Either l r -> Bool
-- | The fromLeft function extracts the element out of a Left
-- and throws an error if its argument is Right. Much like
-- fromJust, using this function in polished code is usually a
-- bad idea.
--
--
-- \x -> fromLeft (Left x) == x
-- \x -> fromLeft (Right x) == undefined
--
fromLeft :: Either l r -> l
-- | The fromRight function extracts the element out of a
-- Right and throws an error if its argument is Left. Much
-- like fromJust, using this function in polished code is
-- usually a bad idea.
--
--
-- \x -> fromRight (Right x) == x
-- \x -> fromRight (Left x) == undefined
--
fromRight :: Either l r -> r
-- | Pull the value out of an Either where both alternatives have
-- the same type.
--
--
-- \x -> fromEither (Left x ) == x
-- \x -> fromEither (Right x) == x
--
fromEither :: Either a a -> a
-- | Extra functions for Control.Monad. These functions provide
-- looping, list operations and booleans. If you need a wider selection
-- of monad loops and list generalisations, see monad-loops.
module Control.Monad.Extra
-- | Perform some operation on Just, given the field inside the
-- Just.
--
--
-- whenJust Nothing print == return ()
-- whenJust (Just 1) print == print 1
--
whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
-- | The identity function which requires the inner argument to be
-- (). Useful for functions with overloaded return times.
--
--
-- \(x :: Maybe ()) -> unit x == x
--
unit :: m () -> m ()
-- | A looping operation, where the predicate returns Left as a seed
-- for the next loop or Right to abort the loop.
loopM :: Monad m => (a -> m (Either a b)) -> a -> m b
-- | Keep running an operation until it becomes False. As an
-- example:
--
--
-- whileM $ do sleep 0.1; notM $ doesFileExist foo.txt
-- readFile foo.txt
--
--
-- If you need some state persisted between each test, use loopM.
whileM :: Monad m => m Bool -> m ()
-- | A version of partition that works with a monadic predicate.
--
--
-- partitionM (Just . even) [1,2,3] == Just ([2], [1,3])
-- partitionM (const Nothing) [1,2,3] == Nothing
--
partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a])
-- | A version of concatMap that works with a monadic predicate.
concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
-- | A version of mapMaybe that works with a monadic predicate.
mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
-- | Like find, but where the test can be monadic.
--
--
-- findM (Just . isUpper) "teST" == Just (Just 'S')
-- findM (Just . isUpper) "test" == Just Nothing
-- findM (Just . const True) ["x",undefined] == Just (Just "x")
--
findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
-- | Like findM, but also allows you to compute some additional
-- information in the predicate.
firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b)
-- | Like when, but where the test can be monadic.
whenM :: Monad m => m Bool -> m () -> m ()
-- | Like unless, but where the test can be monadic.
unlessM :: Monad m => m Bool -> m () -> m ()
-- | Like if, but where the test can be monadic.
ifM :: Monad m => m Bool -> m a -> m a -> m a
-- | Like not, but where the test can be monadic.
notM :: Functor m => m Bool -> m Bool
-- | The lazy || operator lifted to a monad. If the first argument
-- evaluates to True the second argument will not be evaluated.
--
--
-- Just True ||^ undefined == Just True
-- Just False ||^ Just True == Just True
-- Just False ||^ Just False == Just False
--
(||^) :: Monad m => m Bool -> m Bool -> m Bool
-- | The lazy && operator lifted to a monad. If the first
-- argument evaluates to False the second argument will not be
-- evaluated.
--
--
-- Just False &&^ undefined == Just False
-- Just True &&^ Just True == Just True
-- Just True &&^ Just False == Just False
--
(&&^) :: Monad m => m Bool -> m Bool -> m Bool
-- | A version of or lifted to a moand. Retains the short-circuiting
-- behaviour.
--
--
-- orM [Just False,Just True ,undefined] == Just True
-- orM [Just False,Just False,undefined] == undefined
-- \xs -> Just (or xs) == orM (map Just xs)
--
orM :: Monad m => [m Bool] -> m Bool
-- | A version of and lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- andM [Just True,Just False,undefined] == Just False
-- andM [Just True,Just True ,undefined] == undefined
-- \xs -> Just (and xs) == andM (map Just xs)
--
andM :: Monad m => [m Bool] -> m Bool
-- | A version of any lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- anyM Just [False,True ,undefined] == Just True
-- anyM Just [False,False,undefined] == undefined
-- \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--
anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
-- | A version of all lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- allM Just [True,False,undefined] == Just False
-- allM Just [True,True ,undefined] == undefined
-- \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--
allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
-- | Extra directory functions. Most of these functions provide cleaned up
-- and generalised versions of getDirectoryContents, see
-- listContents for the differences.
module System.Directory.Extra
-- | Set the current directory, perform an operation, then change back.
-- Remember that the current directory is a global variable, so calling
-- this function multithreaded is almost certain to go wrong. Avoid
-- changing the current directory if you can.
--
--
-- withTempDir $ \dir -> do writeFile (dir </> "foo.txt") ""; withCurrentDirectory dir $ doesFileExist "foo.txt"
--
withCurrentDirectory :: FilePath -> IO a -> IO a
-- | Create a directory with permissions so that only the current user can
-- view it. On Windows this function is equivalent to
-- createDirectory.
createDirectoryPrivate :: String -> IO ()
-- | List the files and directories directly within a directory. Each
-- result will be prefixed by the query directory, and the special
-- directories . and .. will be ignored. Intended as a
-- cleaned up version of getDirectoryContents.
--
--
-- withTempDir $ \dir -> do writeFile (dir </> "test.txt") ""; (== [dir </> "test.txt"]) <$> listContents dir
-- let touch = mapM_ $ \x -> createDirectoryIfMissing True (takeDirectory x) >> writeFile x ""
-- let listTest op as bs = withTempDir $ \dir -> do touch $ map (dir </>) as; res <- op dir; return $ map (drop (length dir + 1)) res == bs
-- listTest listContents ["bar.txt","foo/baz.txt","zoo"] ["bar.txt","foo","zoo"]
--
listContents :: FilePath -> IO [FilePath]
-- | Like listContents, but only returns the files in a directory,
-- not other directories. Each file will be prefixed by the query
-- directory.
--
--
-- listTest listFiles ["bar.txt","foo/baz.txt","zoo"] ["bar.txt","zoo"]
--
listFiles :: FilePath -> IO [FilePath]
-- | Like listFilesRecursive, but with a predicate to decide where
-- to recurse into. Typically directories starting with . would
-- be ignored. The initial argument directory will have the test applied
-- to it.
--
--
-- listTest (listFilesInside $ return . not . isPrefixOf "." . takeFileName)
-- ["bar.txt","foo" </> "baz.txt",".foo" </> "baz2.txt", "zoo"] ["bar.txt","zoo","foo" </> "baz.txt"]
-- listTest (listFilesInside $ const $ return False) ["bar.txt"] []
--
listFilesInside :: (FilePath -> IO Bool) -> FilePath -> IO [FilePath]
-- | Like listFiles, but goes recursively through all
-- subdirectories.
--
--
-- listTest listFilesRecursive ["bar.txt","zoo","foo" </> "baz.txt"] ["bar.txt","zoo","foo" </> "baz.txt"]
--
listFilesRecursive :: FilePath -> IO [FilePath]
-- | Extra functions for Control.Exception. These functions provide
-- retrying, showing in the presence of exceptions, and functions to
-- catch/ignore exceptions, including monomorphic (no Exception
-- context) versions.
module Control.Exception.Extra
-- | Retry an operation at most n times (n must be positive).
-- If the operation fails the nth time it will throw that final
-- exception.
--
--
-- retry 1 (print "x") == print "x"
-- retry 3 (fail "die") == fail "die"
--
retry :: Int -> IO a -> IO a
-- | Show a value, but if the result contains exceptions, produce
-- <Exception>. Defined as stringException .
-- show. Particularly useful for printing exceptions to users,
-- remembering that exceptions can themselves contain undefined values.
showException :: Show e => e -> IO String
-- | Fully evaluate an input String. If the String contains embedded
-- exceptions it will produce <Exception>.
--
--
-- stringException "test" == return "test"
-- stringException ("test" ++ undefined) == return "test<Exception>"
-- stringException ("test" ++ undefined ++ "hello") == return "test<Exception>"
-- stringException ['t','e','s','t',undefined] == return "test<Exception>"
--
stringException :: String -> IO String
-- | Ignore any exceptions thrown by the action.
--
--
-- ignore (print 1) == print 1
-- ignore (fail "die") == return ()
--
ignore :: IO () -> IO ()
-- | A version of catch without the Exception context,
-- restricted to SomeException, so catches all exceptions.
catch_ :: IO a -> (SomeException -> IO a) -> IO a
-- | Like catch_ but for handle
handle_ :: (SomeException -> IO a) -> IO a -> IO a
-- | Like catch_ but for try
try_ :: IO a -> IO (Either SomeException a)
-- | Like catch_ but for catchJust
catchJust_ :: (SomeException -> Maybe b) -> IO a -> (b -> IO a) -> IO a
-- | Like catch_ but for handleJust
handleJust_ :: (SomeException -> Maybe b) -> (b -> IO a) -> IO a -> IO a
-- | Like catch_ but for tryJust
tryJust_ :: (SomeException -> Maybe b) -> IO a -> IO (Either b a)
-- | Catch an exception if the predicate passes, then call the handler with
-- the original exception. As an example:
--
--
-- readFileExists x == catchBool isDoesNotExistError (readFile "myfile") (const $ return "")
--
catchBool :: Exception e => (e -> Bool) -> IO a -> (e -> IO a) -> IO a
-- | Like catchBool but for handle.
handleBool :: Exception e => (e -> Bool) -> (e -> IO a) -> IO a -> IO a
-- | Like catchBool but for try.
tryBool :: Exception e => (e -> Bool) -> IO a -> IO (Either e a)
-- | Extra functions for Control.Concurrent.
--
-- This module includes three new types of MVar, namely
-- Lock (no associated value), Var (never empty) and
-- Barrier (filled at most once). See this blog post for
-- examples and justification.
--
-- If you need greater control of exceptions and threads see the
-- slave-thread package. If you need elaborate relationships
-- between threads see the async package.
module Control.Concurrent.Extra
-- | Returns the number of Haskell threads that can run truly
-- simultaneously (on separate physical processors) at any given time. To
-- change this value, use setNumCapabilities.
getNumCapabilities :: IO Int
-- | Set the number of Haskell threads that can run truly simultaneously
-- (on separate physical processors) at any given time. The number passed
-- to forkOn is interpreted modulo this value. The initial value
-- is given by the +RTS -N runtime flag.
--
-- This is also the number of threads that will participate in parallel
-- garbage collection. It is strongly recommended that the number of
-- capabilities is not set larger than the number of physical processor
-- cores, and it may often be beneficial to leave one or more cores free
-- to avoid contention with other processes in the machine.
setNumCapabilities :: Int -> IO ()
-- | On GHC 7.6 and above with the -threaded flag, brackets a call
-- to setNumCapabilities. On lower versions (which lack
-- setNumCapabilities) this function just runs the argument
-- action.
withNumCapabilities :: Int -> IO a -> IO a
-- | fork a thread and call the supplied function when the thread is about
-- to terminate, with an exception or a returned value. The function is
-- called with asynchronous exceptions masked.
--
--
-- forkFinally action and_then =
-- mask $ \restore ->
-- forkIO $ try (restore action) >>= and_then
--
--
-- This function is useful for informing the parent when a child
-- terminates, for example.
forkFinally :: IO a -> (Either SomeException a -> IO ()) -> IO ThreadId
-- | Given an action, produce a wrapped action that runs at most once. If
-- the function raises an exception, the same exception will be reraised
-- each time.
once :: IO a -> IO (IO a)
-- | Like an MVar, but has no value. Used to guarantees single-threaded
-- access, typically to some system resource. As an example:
--
--
-- lock <- newLock
-- let output = withLock . putStrLn
-- forkIO $ do ...; output "hello"
-- forkIO $ do ...; output "world"
--
--
-- Here we are creating a lock to ensure that when writing output our
-- messages do not get interleaved. This use of MVar never blocks on a
-- put. It is permissible, but rare, that a withLock contains a withLock
-- inside it - but if so, watch out for deadlocks.
data Lock
-- | Create a new Lock.
newLock :: IO Lock
-- | Perform some operation while holding Lock. Will prevent all
-- other operations from using the Lock while the action is
-- ongoing.
withLock :: Lock -> IO a -> IO a
-- | Like withLock but will never block. If the operation cannot be
-- executed immediately it will return Nothing.
withLockTry :: Lock -> IO a -> IO (Maybe a)
-- | Like an MVar, but must always be full. Used to on a mutable variable
-- in a thread-safe way. As an example:
--
--
-- hits <- newVar 0
-- forkIO $ do ...; modifyVar_ hits (+1); ...
-- i <- readVar hits
-- print (HITS,i)
--
--
-- Here we have a variable which we modify atomically, so modifications
-- are not interleaved. This use of MVar never blocks on a put. No
-- modifyVar operation should ever block, and they should always complete
-- in a reasonable timeframe. A Var should not be used to protect some
-- external resource, only the variable contained within. Information
-- from a readVar should not be subsequently inserted back into the Var.
data Var a
-- | Create a new Var with a value.
newVar :: a -> IO (Var a)
-- | Read the current value of the Var.
readVar :: Var a -> IO a
-- | Modify a Var producing a new value and a return result.
modifyVar :: Var a -> (a -> IO (a, b)) -> IO b
-- | Modify a Var, a restricted version of modifyVar.
modifyVar_ :: Var a -> (a -> IO a) -> IO ()
-- | Perform some operation using the value in the Var, a restricted
-- version of modifyVar.
withVar :: Var a -> (a -> IO b) -> IO b
-- | Starts out empty, then is filled exactly once. As an example:
--
--
-- bar <- newBarrier
-- forkIO $ do ...; val <- ...; signalBarrier bar val
-- print =<< waitBarrier bar
--
--
-- Here we create a barrier which will contain some computed value. A
-- thread is forked to fill the barrier, while the main thread waits for
-- it to complete. A barrier has similarities to a future or promise from
-- other languages, has been known as an IVar in other Haskell work, and
-- in some ways is like a manually managed thunk.
data Barrier a
-- | Create a new Barrier.
newBarrier :: IO (Barrier a)
-- | Write a value into the Barrier, releasing anyone at
-- waitBarrier. Any subsequent attempts to signal the
-- Barrier will be silently ignored.
signalBarrier :: Barrier a -> a -> IO ()
-- | Wait until a barrier has been signaled with signalBarrier.
waitBarrier :: Barrier a -> IO a
-- | A version of waitBarrier that never blocks, returning
-- Nothing if the barrier has not yet been signaled.
waitBarrierMaybe :: Barrier a -> IO (Maybe a)
-- | More IO functions. The functions include ones for reading files with
-- specific encodings, strictly reading files, and writing files with
-- encodings. There are also some simple temporary file functions, more
-- advanced alternatives can be found in the exceptions package.
module System.IO.Extra
-- | Capture the stdout and stderr of a computation.
--
--
-- captureOutput (print 1) == return ("1\n",())
--
captureOutput :: IO a -> IO (String, a)
-- | Execute an action with a custom BufferMode, a warpper around
-- hSetBuffering.
withBuffering :: Handle -> BufferMode -> IO a -> IO a
-- | Like readFile, but setting an encoding.
readFileEncoding :: TextEncoding -> FilePath -> IO String
-- | Like readFile, but with the encoding utf8.
readFileUTF8 :: FilePath -> IO String
-- | Like readFile, but for binary files.
readFileBinary :: FilePath -> IO String
-- | A strict version of readFile. When the string is produced, the
-- entire file will have been read into memory and the file handle will
-- have been closed. Closing the file handle does not rely on the garbage
-- collector.
readFile' :: FilePath -> IO String
-- | A strict version of readFileEncoding, see readFile' for
-- details.
readFileEncoding' :: TextEncoding -> FilePath -> IO String
-- | A strict version of readFileUTF8, see readFile' for
-- details.
readFileUTF8' :: FilePath -> IO String
-- | A strict version of readFileBinary, see readFile' for
-- details.
readFileBinary' :: FilePath -> IO String
-- | Write a file with a particular encoding.
writeFileEncoding :: TextEncoding -> FilePath -> String -> IO ()
-- | Write a file with the utf8 encoding.
writeFileUTF8 :: FilePath -> String -> IO ()
-- | Write a binary file.
writeFileBinary :: FilePath -> String -> IO ()
-- | Create a temporary file in the temporary directory. The file will be
-- deleted after the action completes (provided the file is not still
-- open). The FilePath will not have any file extension, will
-- exist, and will be zero bytes long. If you require a file with a
-- specific name, use withTempDir.
--
--
-- withTempFile doesFileExist == return True
-- (doesFileExist =<< withTempFile return) == return False
-- withTempFile readFile' == return ""
--
withTempFile :: (FilePath -> IO a) -> IO a
-- | Create a temporary directory inside the system temporary directory.
-- The directory will be deleted after the action completes.
--
--
-- withTempDir doesDirectoryExist == return True
-- (doesDirectoryExist =<< withTempDir return) == return False
-- withTempDir listFiles == return []
--
withTempDir :: (FilePath -> IO a) -> IO a
-- | Provide a function to create a temporary file, and a way to delete a
-- temporary file. Most users should use withTempFile which
-- combines these operations.
newTempFile :: IO (FilePath, IO ())
-- | Provide a function to create a temporary directory, and a way to
-- delete a temporary directory. Most users should use withTempDir
-- which combines these operations.
newTempDir :: IO (FilePath, IO ())
-- | Extra functions for creating processes. Specifically variants that
-- automatically check the ExitCode and capture the
-- 'stdout'\/'stderr' handles.
module System.Process.Extra
-- | A version of system that throws an error if the ExitCode
-- is not ExitSuccess.
system_ :: String -> IO ()
-- | A version of system that also captures the output, both
-- stdout and stderr. Returns a pair of the ExitCode
-- and the output.
systemOutput :: String -> IO (ExitCode, String)
-- | A version of system that captures the output (both
-- stdout and stderr) and throws an error if the
-- ExitCode is not ExitSuccess.
systemOutput_ :: String -> IO String
-- | This module documents all the functions available in this package.
--
-- Most users should import the specific modules (e.g.
-- Data.List.Extra), which also reexport their
-- non-Extra modules (e.g. Data.List).
module Extra
-- | Returns the number of Haskell threads that can run truly
-- simultaneously (on separate physical processors) at any given time. To
-- change this value, use setNumCapabilities.
getNumCapabilities :: IO Int
-- | Set the number of Haskell threads that can run truly simultaneously
-- (on separate physical processors) at any given time. The number passed
-- to forkOn is interpreted modulo this value. The initial value
-- is given by the +RTS -N runtime flag.
--
-- This is also the number of threads that will participate in parallel
-- garbage collection. It is strongly recommended that the number of
-- capabilities is not set larger than the number of physical processor
-- cores, and it may often be beneficial to leave one or more cores free
-- to avoid contention with other processes in the machine.
setNumCapabilities :: Int -> IO ()
-- | On GHC 7.6 and above with the -threaded flag, brackets a call
-- to setNumCapabilities. On lower versions (which lack
-- setNumCapabilities) this function just runs the argument
-- action.
withNumCapabilities :: Int -> IO a -> IO a
-- | fork a thread and call the supplied function when the thread is about
-- to terminate, with an exception or a returned value. The function is
-- called with asynchronous exceptions masked.
--
--
-- forkFinally action and_then =
-- mask $ \restore ->
-- forkIO $ try (restore action) >>= and_then
--
--
-- This function is useful for informing the parent when a child
-- terminates, for example.
forkFinally :: IO a -> (Either SomeException a -> IO ()) -> IO ThreadId
-- | Given an action, produce a wrapped action that runs at most once. If
-- the function raises an exception, the same exception will be reraised
-- each time.
once :: IO a -> IO (IO a)
-- | Like an MVar, but has no value. Used to guarantees single-threaded
-- access, typically to some system resource. As an example:
--
--
-- lock <- newLock
-- let output = withLock . putStrLn
-- forkIO $ do ...; output "hello"
-- forkIO $ do ...; output "world"
--
--
-- Here we are creating a lock to ensure that when writing output our
-- messages do not get interleaved. This use of MVar never blocks on a
-- put. It is permissible, but rare, that a withLock contains a withLock
-- inside it - but if so, watch out for deadlocks.
data Lock
-- | Create a new Lock.
newLock :: IO Lock
-- | Perform some operation while holding Lock. Will prevent all
-- other operations from using the Lock while the action is
-- ongoing.
withLock :: Lock -> IO a -> IO a
-- | Like withLock but will never block. If the operation cannot be
-- executed immediately it will return Nothing.
withLockTry :: Lock -> IO a -> IO (Maybe a)
-- | Like an MVar, but must always be full. Used to on a mutable variable
-- in a thread-safe way. As an example:
--
--
-- hits <- newVar 0
-- forkIO $ do ...; modifyVar_ hits (+1); ...
-- i <- readVar hits
-- print (HITS,i)
--
--
-- Here we have a variable which we modify atomically, so modifications
-- are not interleaved. This use of MVar never blocks on a put. No
-- modifyVar operation should ever block, and they should always complete
-- in a reasonable timeframe. A Var should not be used to protect some
-- external resource, only the variable contained within. Information
-- from a readVar should not be subsequently inserted back into the Var.
data Var a
-- | Create a new Var with a value.
newVar :: a -> IO (Var a)
-- | Read the current value of the Var.
readVar :: Var a -> IO a
-- | Modify a Var producing a new value and a return result.
modifyVar :: Var a -> (a -> IO (a, b)) -> IO b
-- | Modify a Var, a restricted version of modifyVar.
modifyVar_ :: Var a -> (a -> IO a) -> IO ()
-- | Perform some operation using the value in the Var, a restricted
-- version of modifyVar.
withVar :: Var a -> (a -> IO b) -> IO b
-- | Starts out empty, then is filled exactly once. As an example:
--
--
-- bar <- newBarrier
-- forkIO $ do ...; val <- ...; signalBarrier bar val
-- print =<< waitBarrier bar
--
--
-- Here we create a barrier which will contain some computed value. A
-- thread is forked to fill the barrier, while the main thread waits for
-- it to complete. A barrier has similarities to a future or promise from
-- other languages, has been known as an IVar in other Haskell work, and
-- in some ways is like a manually managed thunk.
data Barrier a
-- | Create a new Barrier.
newBarrier :: IO (Barrier a)
-- | Write a value into the Barrier, releasing anyone at
-- waitBarrier. Any subsequent attempts to signal the
-- Barrier will be silently ignored.
signalBarrier :: Barrier a -> a -> IO ()
-- | Wait until a barrier has been signaled with signalBarrier.
waitBarrier :: Barrier a -> IO a
-- | A version of waitBarrier that never blocks, returning
-- Nothing if the barrier has not yet been signaled.
waitBarrierMaybe :: Barrier a -> IO (Maybe a)
-- | Retry an operation at most n times (n must be positive).
-- If the operation fails the nth time it will throw that final
-- exception.
--
--
-- retry 1 (print "x") == print "x"
-- retry 3 (fail "die") == fail "die"
--
retry :: Int -> IO a -> IO a
-- | Show a value, but if the result contains exceptions, produce
-- <Exception>. Defined as stringException .
-- show. Particularly useful for printing exceptions to users,
-- remembering that exceptions can themselves contain undefined values.
showException :: Show e => e -> IO String
-- | Fully evaluate an input String. If the String contains embedded
-- exceptions it will produce <Exception>.
--
--
-- stringException "test" == return "test"
-- stringException ("test" ++ undefined) == return "test<Exception>"
-- stringException ("test" ++ undefined ++ "hello") == return "test<Exception>"
-- stringException ['t','e','s','t',undefined] == return "test<Exception>"
--
stringException :: String -> IO String
-- | Ignore any exceptions thrown by the action.
--
--
-- ignore (print 1) == print 1
-- ignore (fail "die") == return ()
--
ignore :: IO () -> IO ()
-- | A version of catch without the Exception context,
-- restricted to SomeException, so catches all exceptions.
catch_ :: IO a -> (SomeException -> IO a) -> IO a
-- | Like catch_ but for handle
handle_ :: (SomeException -> IO a) -> IO a -> IO a
-- | Like catch_ but for try
try_ :: IO a -> IO (Either SomeException a)
-- | Like catch_ but for catchJust
catchJust_ :: (SomeException -> Maybe b) -> IO a -> (b -> IO a) -> IO a
-- | Like catch_ but for handleJust
handleJust_ :: (SomeException -> Maybe b) -> (b -> IO a) -> IO a -> IO a
-- | Like catch_ but for tryJust
tryJust_ :: (SomeException -> Maybe b) -> IO a -> IO (Either b a)
-- | Catch an exception if the predicate passes, then call the handler with
-- the original exception. As an example:
--
--
-- readFileExists x == catchBool isDoesNotExistError (readFile "myfile") (const $ return "")
--
catchBool :: Exception e => (e -> Bool) -> IO a -> (e -> IO a) -> IO a
-- | Like catchBool but for handle.
handleBool :: Exception e => (e -> Bool) -> (e -> IO a) -> IO a -> IO a
-- | Like catchBool but for try.
tryBool :: Exception e => (e -> Bool) -> IO a -> IO (Either e a)
-- | Perform some operation on Just, given the field inside the
-- Just.
--
--
-- whenJust Nothing print == return ()
-- whenJust (Just 1) print == print 1
--
whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
-- | The identity function which requires the inner argument to be
-- (). Useful for functions with overloaded return times.
--
--
-- \(x :: Maybe ()) -> unit x == x
--
unit :: m () -> m ()
-- | A looping operation, where the predicate returns Left as a seed
-- for the next loop or Right to abort the loop.
loopM :: Monad m => (a -> m (Either a b)) -> a -> m b
-- | Keep running an operation until it becomes False. As an
-- example:
--
--
-- whileM $ do sleep 0.1; notM $ doesFileExist foo.txt
-- readFile foo.txt
--
--
-- If you need some state persisted between each test, use loopM.
whileM :: Monad m => m Bool -> m ()
-- | A version of partition that works with a monadic predicate.
--
--
-- partitionM (Just . even) [1,2,3] == Just ([2], [1,3])
-- partitionM (const Nothing) [1,2,3] == Nothing
--
partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a])
-- | A version of concatMap that works with a monadic predicate.
concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
-- | A version of mapMaybe that works with a monadic predicate.
mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
-- | Like find, but where the test can be monadic.
--
--
-- findM (Just . isUpper) "teST" == Just (Just 'S')
-- findM (Just . isUpper) "test" == Just Nothing
-- findM (Just . const True) ["x",undefined] == Just (Just "x")
--
findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
-- | Like findM, but also allows you to compute some additional
-- information in the predicate.
firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b)
-- | Like when, but where the test can be monadic.
whenM :: Monad m => m Bool -> m () -> m ()
-- | Like unless, but where the test can be monadic.
unlessM :: Monad m => m Bool -> m () -> m ()
-- | Like if, but where the test can be monadic.
ifM :: Monad m => m Bool -> m a -> m a -> m a
-- | Like not, but where the test can be monadic.
notM :: Functor m => m Bool -> m Bool
-- | The lazy || operator lifted to a monad. If the first argument
-- evaluates to True the second argument will not be evaluated.
--
--
-- Just True ||^ undefined == Just True
-- Just False ||^ Just True == Just True
-- Just False ||^ Just False == Just False
--
(||^) :: Monad m => m Bool -> m Bool -> m Bool
-- | The lazy && operator lifted to a monad. If the first
-- argument evaluates to False the second argument will not be
-- evaluated.
--
--
-- Just False &&^ undefined == Just False
-- Just True &&^ Just True == Just True
-- Just True &&^ Just False == Just False
--
(&&^) :: Monad m => m Bool -> m Bool -> m Bool
-- | A version of or lifted to a moand. Retains the short-circuiting
-- behaviour.
--
--
-- orM [Just False,Just True ,undefined] == Just True
-- orM [Just False,Just False,undefined] == undefined
-- \xs -> Just (or xs) == orM (map Just xs)
--
orM :: Monad m => [m Bool] -> m Bool
-- | A version of and lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- andM [Just True,Just False,undefined] == Just False
-- andM [Just True,Just True ,undefined] == undefined
-- \xs -> Just (and xs) == andM (map Just xs)
--
andM :: Monad m => [m Bool] -> m Bool
-- | A version of any lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- anyM Just [False,True ,undefined] == Just True
-- anyM Just [False,False,undefined] == undefined
-- \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--
anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
-- | A version of all lifted to a moand. Retains the
-- short-circuiting behaviour.
--
--
-- allM Just [True,False,undefined] == Just False
-- allM Just [True,True ,undefined] == undefined
-- \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--
allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
-- | Test if an Either value is the Left constructor.
-- Provided as standard with GHC 7.8 and above.
isLeft :: Either l r -> Bool
-- | Test if an Either value is the Right constructor.
-- Provided as standard with GHC 7.8 and above.
isRight :: Either l r -> Bool
-- | The fromLeft function extracts the element out of a Left
-- and throws an error if its argument is Right. Much like
-- fromJust, using this function in polished code is usually a
-- bad idea.
--
--
-- \x -> fromLeft (Left x) == x
-- \x -> fromLeft (Right x) == undefined
--
fromLeft :: Either l r -> l
-- | The fromRight function extracts the element out of a
-- Right and throws an error if its argument is Left. Much
-- like fromJust, using this function in polished code is
-- usually a bad idea.
--
--
-- \x -> fromRight (Right x) == x
-- \x -> fromRight (Left x) == undefined
--
fromRight :: Either l r -> r
-- | Pull the value out of an Either where both alternatives have
-- the same type.
--
--
-- \x -> fromEither (Left x ) == x
-- \x -> fromEither (Right x) == x
--
fromEither :: Either a a -> a
-- | Strict version of modifyIORef
modifyIORef' :: IORef a -> (a -> a) -> IO ()
-- | Evaluates the value before calling writeIORef.
writeIORef' :: IORef a -> a -> IO ()
-- | Strict version of atomicModifyIORef. This forces both the value
-- stored in the IORef as well as the value returned.
atomicModifyIORef' :: IORef a -> (a -> (a, b)) -> IO b
-- | Variant of writeIORef with the "barrier to reordering" property
-- that atomicModifyIORef has.
atomicWriteIORef :: IORef a -> a -> IO ()
-- | Evaluates the value before calling atomicWriteIORef.
atomicWriteIORef' :: IORef a -> a -> IO ()
-- | Convert a string to lower case.
--
--
-- lower "This is A TEST" == "this is a test"
-- lower "" == ""
--
lower :: String -> String
-- | Convert a string to upper case.
--
--
-- upper "This is A TEST" == "THIS IS A TEST"
-- upper "" == ""
--
upper :: String -> String
-- | Remove spaces from either side of a string. A combination of
-- trimEnd and trimStart.
--
--
-- trim " hello " == "hello"
-- trimStart " hello " == "hello "
-- trimEnd " hello " == " hello"
-- \s -> trim s == trimEnd (trimStart s)
--
trim :: String -> String
-- | Remove spaces from the start of a string, see trim.
trimStart :: String -> String
-- | Remove spaces from the end of a string, see trim.
trimEnd :: String -> String
-- | Split the first word off a string. Useful for when starting to parse
-- the beginning of a string, but you want to accurately perserve
-- whitespace in the rest of the string.
--
--
-- word1 "" == ("", "")
-- word1 "keyword rest of string" == ("keyword","rest of string")
-- word1 " keyword\n rest of string" == ("keyword","rest of string")
-- \s -> fst (word1 s) == concat (take 1 $ words s)
-- \s -> words (snd $ word1 s) == drop 1 (words s)
--
word1 :: String -> (String, String)
-- | Drop a number of elements from the end of the list.
--
--
-- dropEnd 3 "hello" == "he"
-- dropEnd 5 "bye" == ""
-- dropEnd (-1) "bye" == "bye"
-- \i xs -> dropEnd i xs `isPrefixOf` xs
-- \i xs -> length (dropEnd i xs) == max 0 (length xs - max 0 i)
-- \i -> take 3 (dropEnd 5 [i..]) == take 3 [i..]
--
dropEnd :: Int -> [a] -> [a]
-- | Take a number of elements from the end of the list.
--
--
-- takeEnd 3 "hello" == "llo"
-- takeEnd 5 "bye" == "bye"
-- takeEnd (-1) "bye" == ""
-- \i xs -> takeEnd i xs `isSuffixOf` xs
-- \i xs -> length (takeEnd i xs) == min (max 0 i) (length xs)
--
takeEnd :: Int -> [a] -> [a]
-- | Break, but from the end.
--
--
-- breakEnd isLower "youRE" == ("you","RE")
-- breakEnd isLower "youre" == ("youre","")
-- breakEnd isLower "YOURE" == ("","YOURE")
--
breakEnd :: (a -> Bool) -> [a] -> ([a], [a])
-- | Span, but from the end.
--
--
-- spanEnd isUpper "youRE" == ("you","RE")
-- spanEnd (not . isSpace) "x y z" == ("x y ","z")
-- \f xs-> spanEnd f xs == swap (both reverse (span f (reverse xs)))
--
spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
-- | The dropWhileEnd function drops the largest suffix of a list in
-- which the given predicate holds for all elements. For example:
--
--
-- dropWhileEnd isSpace "foo\n" == "foo"
-- dropWhileEnd isSpace "foo bar" == "foo bar"
-- dropWhileEnd isSpace ("foo\n" ++ undefined) == "foo" ++ undefined
--
dropWhileEnd :: (a -> Bool) -> [a] -> [a]
-- | A version of dropWhileEnd but with different strictness
-- properties. The function dropWhileEnd can be used on an
-- infinite list and tests the property on each character. In contrast,
-- dropWhileEnd' is strict in the spine of the list but only tests
-- the trailing suffix. This version usually outperforms
-- dropWhileEnd if the list is short or the test is expensive.
-- Note the tests below cover both the prime and non-prime variants.
--
--
-- dropWhileEnd isSpace "ab cde " == "ab cde"
-- dropWhileEnd' isSpace "ab cde " == "ab cde"
-- last (dropWhileEnd even [undefined,3]) == undefined
-- last (dropWhileEnd' even [undefined,3]) == 3
-- head (dropWhileEnd even (3:undefined)) == 3
-- head (dropWhileEnd' even (3:undefined)) == undefined
--
dropWhileEnd' :: (a -> Bool) -> [a] -> [a]
-- | A version of takeWhile operating from the end.
--
--
-- takeWhileEnd even [2,3,4,6] == [4,6]
--
takeWhileEnd :: (a -> Bool) -> [a] -> [a]
-- | Return the prefix of the second string if its suffix matches the
-- entire first string.
--
-- Examples:
--
--
-- stripSuffix "bar" "foobar" == Just "foo"
-- stripSuffix "" "baz" == Just "baz"
-- stripSuffix "foo" "quux" == Nothing
--
stripSuffix :: Eq a => [a] -> [a] -> Maybe [a]
-- | A variant of words with a custom test. In particular, adjacent
-- separators are discarded, as are leading or trailing separators.
--
--
-- wordsBy (== ':') "::xyz:abc::123::" == ["xyz","abc","123"]
-- \s -> wordsBy isSpace s == words s
--
wordsBy :: (a -> Bool) -> [a] -> [[a]]
-- | A variant of lines with a custom test. In particular, if there
-- is a trailing separator it will be discarded.
--
--
-- linesBy (== ':') "::xyz:abc::123::" == ["","","xyz","abc","","123",""]
-- \s -> linesBy (== '\n') s == lines s
-- linesBy (== ';') "my;list;here;" == ["my","list","here"]
--
linesBy :: (a -> Bool) -> [a] -> [[a]]
-- | Find the first instance of needle in haystack. The
-- first element of the returned tuple is the prefix of haystack
-- before needle is matched. The second is the remainder of
-- haystack, starting with the match.
--
--
-- breakOn "::" "a::b::c" == ("a", "::b::c")
-- breakOn "/" "foobar" == ("foobar", "")
-- \needle haystack -> let (prefix,match) = breakOn needle haystack in prefix ++ match == haystack
--
breakOn :: Eq a => [a] -> [a] -> ([a], [a])
-- | Similar to breakOn, but searches from the end of the string.
--
-- The first element of the returned tuple is the prefix of
-- haystack up to and including the last match of
-- needle. The second is the remainder of haystack,
-- following the match.
--
--
-- breakOnEnd "::" "a::b::c" == ("a::b::", "c")
--
breakOnEnd :: Eq a => [a] -> [a] -> ([a], [a])
-- | Break a list into pieces separated by the first list argument,
-- consuming the delimiter. An empty delimiter is invalid, and will cause
-- an error to be raised.
--
--
-- splitOn "\r\n" "a\r\nb\r\nd\r\ne" == ["a","b","d","e"]
-- splitOn "aaa" "aaaXaaaXaaaXaaa" == ["","X","X","X",""]
-- splitOn "x" "x" == ["",""]
-- splitOn "x" "" == [""]
-- \s x -> s /= "" ==> intercalate s (splitOn s x) == x
-- \c x -> splitOn [c] x == split (==c) x
--
splitOn :: Eq a => [a] -> [a] -> [[a]]
-- | Splits a list into components delimited by separators, where the
-- predicate returns True for a separator element. The resulting
-- components do not contain the separators. Two adjacent separators
-- result in an empty component in the output.
--
--
-- split (== 'a') "aabbaca" == ["","","bb","c",""]
-- split (== 'a') "" == [""]
-- split (== ':') "::xyz:abc::123::" == ["","","xyz","abc","","123","",""]
-- split (== ',') "my,list,here" == ["my","list","here"]
--
split :: (a -> Bool) -> [a] -> [[a]]
-- | Split a list into chunks of a given size. The last chunk may contain
-- fewer than n elements. The chunk size must be positive.
--
--
-- chunksOf 3 "my test" == ["my ","tes","t"]
-- chunksOf 3 "mytest" == ["myt","est"]
-- chunksOf 8 "" == []
-- chunksOf 0 "test" == undefined
--
chunksOf :: Int -> [a] -> [[a]]
-- | Non-recursive transform over a list, like maybe.
--
--
-- list 1 (\v _ -> v - 2) [5,6,7] == 3
-- list 1 (\v _ -> v - 2) [] == 1
-- \nil cons xs -> maybe nil (uncurry cons) (uncons xs) == list nil cons xs
--
list :: b -> (a -> [a] -> b) -> [a] -> b
-- | If the list is empty returns Nothing, otherwise returns the
-- head and the tail.
--
--
-- uncons "test" == Just ('t',"est")
-- uncons "" == Nothing
-- \xs -> uncons xs == if null xs then Nothing else Just (head xs, tail xs)
--
uncons :: [a] -> Maybe (a, [a])
-- | If the list is empty returns Nothing, otherwise returns the
-- init and the last.
--
--
-- unsnoc "test" == Just ("tes",'t')
-- unsnoc "" == Nothing
-- \xs -> unsnoc xs == if null xs then Nothing else Just (init xs, last xs)
--
unsnoc :: [a] -> Maybe ([a], a)
-- | Append an element to the start of a list, an alias for '(:)'.
--
--
-- cons 't' "est" == "test"
-- \x xs -> uncons (cons x xs) == Just (x,xs)
--
cons :: a -> [a] -> [a]
-- | Append an element to the end of a list, takes O(n) time.
--
--
-- snoc "tes" 't' == "test"
-- \xs x -> unsnoc (snoc xs x) == Just (xs,x)
--
snoc :: [a] -> a -> [a]
-- | Equivalent to drop 1, but likely to be faster and a single
-- lexeme.
--
--
-- drop1 "" == ""
-- drop1 "test" == "est"
-- \xs -> drop 1 xs == drop1 xs
--
drop1 :: [a] -> [a]
-- | A combination of group and sort.
--
--
-- groupSort [(1,'t'),(3,'t'),(2,'e'),(2,'s')] == [(1,"t"),(2,"es"),(3,"t")]
-- \xs -> map fst (groupSort xs) == sort (nub (map fst xs))
-- \xs -> concatMap snd (groupSort xs) == map snd (sortOn fst xs)
--
groupSort :: Ord k => [(k, v)] -> [(k, [v])]
-- | A version of nub where the equality is done on some extracted
-- value. nubOn f is equivalent to nubBy ((==) on
-- f), but has the performance advantage of only evaluating
-- f once for each element in the input list.
nubOn :: Eq b => (a -> b) -> [a] -> [a]
-- | A version of group where the equality is done on some extracted
-- value.
groupOn :: Eq b => (a -> b) -> [a] -> [[a]]
-- | Sort a list by comparing the results of a key function applied to each
-- element. sortOn f is equivalent to sortBy (comparing
-- f), but has the performance advantage of only evaluating
-- f once for each element in the input list. This is called the
-- decorate-sort-undecorate paradigm, or Schwartzian transform.
--
--
-- sortOn fst [(3,"z"),(1,""),(3,"a")] == [(1,""),(3,"z"),(3,"a")]
--
sortOn :: Ord b => (a -> b) -> [a] -> [a]
-- | Are two lists disjoint, with no elements in common.
--
--
-- disjoint [1,2,3] [4,5] == True
-- disjoint [1,2,3] [4,1] == False
--
disjoint :: Eq a => [a] -> [a] -> Bool
-- | Are all elements the same.
--
--
-- allSame [1,1,2] == False
-- allSame [1,1,1] == True
-- allSame [1] == True
-- allSame [] == True
-- allSame (1:1:2:undefined) == False
-- \xs -> allSame xs == (length (nub xs) <= 1)
--
allSame :: Eq a => [a] -> Bool
-- | Is there any element which occurs more than once.
--
--
-- anySame [1,1,2] == True
-- anySame [1,2,3] == False
-- anySame (1:2:1:undefined) == True
-- anySame [] == False
-- \xs -> anySame xs == (length (nub xs) < length xs)
--
anySame :: Eq a => [a] -> Bool
-- | Apply some operation repeatedly, producing an element of output and
-- the remainder of the list.
--
--
-- \xs -> repeatedly (splitAt 3) xs == chunksOf 3 xs
-- \xs -> repeatedly word1 (trim xs) == words xs
--
repeatedly :: ([a] -> (b, [a])) -> [a] -> [b]
-- | Flipped version of map.
--
--
-- for [1,2,3] (+1) == [2,3,4]
--
for :: [a] -> (a -> b) -> [b]
-- | Find the first element of a list for which the operation returns
-- Just, along with the result of the operation. Like find
-- but useful where the function also computes some expensive information
-- that can be reused. Particular useful when the function is monadic,
-- see firstJustM.
--
--
-- firstJust id [Nothing,Just 3] == Just 3
-- firstJust id [Nothing,Nothing] == Nothing
--
firstJust :: (a -> Maybe b) -> [a] -> Maybe b
-- | A merging of unzip and concat.
--
--
-- concatUnzip [("a","AB"),("bc","C")] == ("abc","ABC")
--
concatUnzip :: [([a], [b])] -> ([a], [b])
-- | A merging of unzip3 and concat.
--
--
-- concatUnzip3 [("a","AB",""),("bc","C","123")] == ("abc","ABC","123")
--
concatUnzip3 :: [([a], [b], [c])] -> ([a], [b], [c])
-- | Replace a subsequence everywhere it occurs. The first argument must
-- not be the empty list.
--
--
-- replace "el" "_" "Hello Bella" == "H_lo B_la"
-- replace "el" "e" "Hello" == "Helo"
-- replace "" "e" "Hello" == undefined
-- \xs ys -> not (null xs) ==> replace xs xs ys == ys
--
replace :: Eq a => [a] -> [a] -> [a] -> [a]
-- | Merge two lists which are assumed to be ordered.
--
--
-- merge "ace" "bd" == "abcde"
-- \xs ys -> merge (sort xs) (sort ys) == sort (xs ++ ys)
--
merge :: Ord a => [a] -> [a] -> [a]
-- | Like merge, but with a custom ordering function.
mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
-- | Update the first component of a pair.
--
--
-- first succ (1,"test") == (2,"test")
--
first :: (a -> a') -> (a, b) -> (a', b)
-- | Update the second component of a pair.
--
--
-- second reverse (1,"test") == (1,"tset")
--
second :: (b -> b') -> (a, b) -> (a, b')
-- | Given two functions, apply one to the first component and one to the
-- second. A specialised version of ***.
--
--
-- (succ *** reverse) (1,"test") == (2,"tset")
--
(***) :: (a -> a') -> (b -> b') -> (a, b) -> (a', b')
-- | Given two functions, apply both to a single argument to form a pair. A
-- specialised version of &&&.
--
--
-- (succ &&& pred) 1 == (2,0)
--
(&&&) :: (a -> b) -> (a -> c) -> a -> (b, c)
-- | Duplicate a single value into a pair.
--
--
-- dupe 12 == (12, 12)
--
dupe :: a -> (a, a)
-- | Apply a single function to both components of a pair.
--
--
-- both succ (1,2) == (2,3)
--
both :: (a -> b) -> (a, a) -> (b, b)
-- | Extract the fst of a triple.
fst3 :: (a, b, c) -> a
-- | Extract the snd of a triple.
snd3 :: (a, b, c) -> b
-- | Extract the final element of a triple.
thd3 :: (a, b, c) -> c
-- | Show a number to a fixed number of decimal places.
--
--
-- showDP 4 pi == "3.1416"
-- showDP 0 pi == "3"
-- showDP 2 3 == "3.00"
--
showDP :: RealFloat a => Int -> a -> String
-- | Specialised numeric conversion, type restricted version of
-- fromIntegral.
intToDouble :: Int -> Double
-- | Specialised numeric conversion, type restricted version of
-- fromIntegral.
intToFloat :: Int -> Float
-- | Specialised numeric conversion, type restricted version of
-- realToFrac.
floatToDouble :: Float -> Double
-- | Specialised numeric conversion, type restricted version of
-- realToFrac.
doubleToFloat :: Double -> Float
-- | Set the current directory, perform an operation, then change back.
-- Remember that the current directory is a global variable, so calling
-- this function multithreaded is almost certain to go wrong. Avoid
-- changing the current directory if you can.
--
--
-- withTempDir $ \dir -> do writeFile (dir </> "foo.txt") ""; withCurrentDirectory dir $ doesFileExist "foo.txt"
--
withCurrentDirectory :: FilePath -> IO a -> IO a
-- | Create a directory with permissions so that only the current user can
-- view it. On Windows this function is equivalent to
-- createDirectory.
createDirectoryPrivate :: String -> IO ()
-- | List the files and directories directly within a directory. Each
-- result will be prefixed by the query directory, and the special
-- directories . and .. will be ignored. Intended as a
-- cleaned up version of getDirectoryContents.
--
--
-- withTempDir $ \dir -> do writeFile (dir </> "test.txt") ""; (== [dir </> "test.txt"]) <$> listContents dir
-- let touch = mapM_ $ \x -> createDirectoryIfMissing True (takeDirectory x) >> writeFile x ""
-- let listTest op as bs = withTempDir $ \dir -> do touch $ map (dir </>) as; res <- op dir; return $ map (drop (length dir + 1)) res == bs
-- listTest listContents ["bar.txt","foo/baz.txt","zoo"] ["bar.txt","foo","zoo"]
--
listContents :: FilePath -> IO [FilePath]
-- | Like listContents, but only returns the files in a directory,
-- not other directories. Each file will be prefixed by the query
-- directory.
--
--
-- listTest listFiles ["bar.txt","foo/baz.txt","zoo"] ["bar.txt","zoo"]
--
listFiles :: FilePath -> IO [FilePath]
-- | Like listFilesRecursive, but with a predicate to decide where
-- to recurse into. Typically directories starting with . would
-- be ignored. The initial argument directory will have the test applied
-- to it.
--
--
-- listTest (listFilesInside $ return . not . isPrefixOf "." . takeFileName)
-- ["bar.txt","foo" </> "baz.txt",".foo" </> "baz2.txt", "zoo"] ["bar.txt","zoo","foo" </> "baz.txt"]
-- listTest (listFilesInside $ const $ return False) ["bar.txt"] []
--
listFilesInside :: (FilePath -> IO Bool) -> FilePath -> IO [FilePath]
-- | Like listFiles, but goes recursively through all
-- subdirectories.
--
--
-- listTest listFilesRecursive ["bar.txt","zoo","foo" </> "baz.txt"] ["bar.txt","zoo","foo" </> "baz.txt"]
--
listFilesRecursive :: FilePath -> IO [FilePath]
-- | Returns the absolute pathname of the current executable.
--
-- Note that for scripts and interactive sessions, this is the path to
-- the interpreter (e.g. ghci.)
getExecutablePath :: IO FilePath
-- | Return the value of the environment variable var, or
-- Nothing if there is no such value.
--
-- For POSIX users, this is equivalent to getEnv.
lookupEnv :: String -> IO (Maybe String)
-- | Return True on Windows and False otherwise. A runtime
-- version of #ifdef minw32_HOST_OS. Equivalent to os ==
-- "mingw32", but: more efficient; doesn't require typing an easily
-- mistypeable string; actually asks about your OS not a library; doesn't
-- bake in 32bit assumptions that are already false. </rant>
--
--
-- isWindows == (os == "mingw32")
--
isWindows :: Bool
-- | Capture the stdout and stderr of a computation.
--
--
-- captureOutput (print 1) == return ("1\n",())
--
captureOutput :: IO a -> IO (String, a)
-- | Execute an action with a custom BufferMode, a warpper around
-- hSetBuffering.
withBuffering :: Handle -> BufferMode -> IO a -> IO a
-- | Like readFile, but setting an encoding.
readFileEncoding :: TextEncoding -> FilePath -> IO String
-- | Like readFile, but with the encoding utf8.
readFileUTF8 :: FilePath -> IO String
-- | Like readFile, but for binary files.
readFileBinary :: FilePath -> IO String
-- | A strict version of readFile. When the string is produced, the
-- entire file will have been read into memory and the file handle will
-- have been closed. Closing the file handle does not rely on the garbage
-- collector.
readFile' :: FilePath -> IO String
-- | A strict version of readFileEncoding, see readFile' for
-- details.
readFileEncoding' :: TextEncoding -> FilePath -> IO String
-- | A strict version of readFileUTF8, see readFile' for
-- details.
readFileUTF8' :: FilePath -> IO String
-- | A strict version of readFileBinary, see readFile' for
-- details.
readFileBinary' :: FilePath -> IO String
-- | Write a file with a particular encoding.
writeFileEncoding :: TextEncoding -> FilePath -> String -> IO ()
-- | Write a file with the utf8 encoding.
writeFileUTF8 :: FilePath -> String -> IO ()
-- | Write a binary file.
writeFileBinary :: FilePath -> String -> IO ()
-- | Create a temporary file in the temporary directory. The file will be
-- deleted after the action completes (provided the file is not still
-- open). The FilePath will not have any file extension, will
-- exist, and will be zero bytes long. If you require a file with a
-- specific name, use withTempDir.
--
--
-- withTempFile doesFileExist == return True
-- (doesFileExist =<< withTempFile return) == return False
-- withTempFile readFile' == return ""
--
withTempFile :: (FilePath -> IO a) -> IO a
-- | Create a temporary directory inside the system temporary directory.
-- The directory will be deleted after the action completes.
--
--
-- withTempDir doesDirectoryExist == return True
-- (doesDirectoryExist =<< withTempDir return) == return False
-- withTempDir listFiles == return []
--
withTempDir :: (FilePath -> IO a) -> IO a
-- | Provide a function to create a temporary file, and a way to delete a
-- temporary file. Most users should use withTempFile which
-- combines these operations.
newTempFile :: IO (FilePath, IO ())
-- | Provide a function to create a temporary directory, and a way to
-- delete a temporary directory. Most users should use withTempDir
-- which combines these operations.
newTempDir :: IO (FilePath, IO ())
-- | A version of system that throws an error if the ExitCode
-- is not ExitSuccess.
system_ :: String -> IO ()
-- | A version of system that also captures the output, both
-- stdout and stderr. Returns a pair of the ExitCode
-- and the output.
systemOutput :: String -> IO (ExitCode, String)
-- | A version of system that captures the output (both
-- stdout and stderr) and throws an error if the
-- ExitCode is not ExitSuccess.
systemOutput_ :: String -> IO String
-- | A type alias for seconds, which are stored as Double.
type Seconds = Double
-- | Sleep for a number of seconds.
--
--
-- fmap (round . fst) (duration $ sleep 1) == return 1
--
sleep :: Seconds -> IO ()
-- | Calculate the difference between two times in seconds. Usually the
-- first time will be the end of an event, and the second time will be
-- the beginning.
--
--
-- \a b -> a > b ==> subtractTime a b > 0
--
subtractTime :: UTCTime -> UTCTime -> Seconds
-- | Show a number of seconds, typically a duration, in a suitable manner
-- with responable precision for a human.
--
--
-- showDuration 3.435 == "3.44s"
-- showDuration 623.8 == "10m24s"
-- showDuration 62003.8 == "17h13m"
-- showDuration 1e8 == "27777h47m"
--
showDuration :: Seconds -> String
-- | Call once to start, then call repeatedly to get the elapsed time since
-- the first call. Values will usually increase, unless the system clock
-- is updated (if you need the guarantee, see offsetTimeIncrease).
offsetTime :: IO (IO Seconds)
-- | Like offsetTime, but results will never decrease (though they
-- may stay the same).
--
--
-- do f <- offsetTimeIncrease; xs <- replicateM 10 f; return $ xs == sort xs
--
offsetTimeIncrease :: IO (IO Seconds)
-- | Record how long a computation takes in Seconds.
duration :: IO a -> IO (Seconds, a)