Safe Haskell | None |
---|---|

Language | Haskell2010 |

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`

).

- getNumCapabilities :: IO Int
- setNumCapabilities :: Int -> IO ()
- withNumCapabilities :: Int -> IO a -> IO a
- forkFinally :: IO a -> (Either SomeException a -> IO ()) -> IO ThreadId
- once :: IO a -> IO (IO a)
- onceFork :: IO a -> IO (IO a)
- data Lock
- newLock :: IO Lock
- withLock :: Lock -> IO a -> IO a
- withLockTry :: Lock -> IO a -> IO (Maybe a)
- data Var a
- newVar :: a -> IO (Var a)
- readVar :: Var a -> IO a
- modifyVar :: Var a -> (a -> IO (a, b)) -> IO b
- modifyVar_ :: Var a -> (a -> IO a) -> IO ()
- withVar :: Var a -> (a -> IO b) -> IO b
- data Barrier a
- newBarrier :: IO (Barrier a)
- signalBarrier :: Barrier a -> a -> IO ()
- waitBarrier :: Barrier a -> IO a
- waitBarrierMaybe :: Barrier a -> IO (Maybe a)
- retry :: Int -> IO a -> IO a
- retryBool :: Exception e => (e -> Bool) -> Int -> IO a -> IO a
- showException :: Show e => e -> IO String
- stringException :: String -> IO String
- errorIO :: String -> IO a
- displayException :: Exception e => e -> String
- ignore :: IO () -> IO ()
- catch_ :: IO a -> (SomeException -> IO a) -> IO a
- handle_ :: (SomeException -> IO a) -> IO a -> IO a
- try_ :: IO a -> IO (Either SomeException a)
- catchJust_ :: (SomeException -> Maybe b) -> IO a -> (b -> IO a) -> IO a
- handleJust_ :: (SomeException -> Maybe b) -> (b -> IO a) -> IO a -> IO a
- tryJust_ :: (SomeException -> Maybe b) -> IO a -> IO (Either b a)
- catchBool :: Exception e => (e -> Bool) -> IO a -> (e -> IO a) -> IO a
- handleBool :: Exception e => (e -> Bool) -> (e -> IO a) -> IO a -> IO a
- tryBool :: Exception e => (e -> Bool) -> IO a -> IO (Either e a)
- whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
- whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m ()
- unit :: m () -> m ()
- maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b
- eitherM :: Monad m => (a -> m c) -> (b -> m c) -> m (Either a b) -> m c
- loopM :: Monad m => (a -> m (Either a b)) -> a -> m b
- whileM :: Monad m => m Bool -> m ()
- partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a])
- concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
- concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b]
- mconcatMapM :: (Monad m, Monoid b) => (a -> m b) -> [a] -> m b
- mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
- findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
- firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b)
- whenM :: Monad m => m Bool -> m () -> m ()
- unlessM :: Monad m => m Bool -> m () -> m ()
- ifM :: Monad m => m Bool -> m a -> m a -> m a
- notM :: Functor m => m Bool -> m Bool
- (||^) :: Monad m => m Bool -> m Bool -> m Bool
- (&&^) :: Monad m => m Bool -> m Bool -> m Bool
- orM :: Monad m => [m Bool] -> m Bool
- andM :: Monad m => [m Bool] -> m Bool
- anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
- allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
- isLeft :: Either a b -> Bool
- isRight :: Either a b -> Bool
- fromLeft :: Either l r -> l
- fromRight :: Either l r -> r
- fromEither :: Either a a -> a
- modifyIORef' :: IORef a -> (a -> a) -> IO ()
- writeIORef' :: IORef a -> a -> IO ()
- atomicModifyIORef' :: IORef a -> (a -> (a, b)) -> IO b
- atomicWriteIORef :: IORef a -> a -> IO ()
- atomicWriteIORef' :: IORef a -> a -> IO ()
- lower :: String -> String
- upper :: String -> String
- trim :: String -> String
- trimStart :: String -> String
- trimEnd :: String -> String
- word1 :: String -> (String, String)
- line1 :: String -> (String, String)
- dropEnd :: Int -> [a] -> [a]
- takeEnd :: Int -> [a] -> [a]
- splitAtEnd :: Int -> [a] -> ([a], [a])
- breakEnd :: (a -> Bool) -> [a] -> ([a], [a])
- spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
- dropWhileEnd :: (a -> Bool) -> [a] -> [a]
- dropWhileEnd' :: (a -> Bool) -> [a] -> [a]
- takeWhileEnd :: (a -> Bool) -> [a] -> [a]
- stripSuffix :: Eq a => [a] -> [a] -> Maybe [a]
- stripInfix :: Eq a => [a] -> [a] -> Maybe ([a], [a])
- stripInfixEnd :: Eq a => [a] -> [a] -> Maybe ([a], [a])
- wordsBy :: (a -> Bool) -> [a] -> [[a]]
- linesBy :: (a -> Bool) -> [a] -> [[a]]
- breakOn :: Eq a => [a] -> [a] -> ([a], [a])
- breakOnEnd :: Eq a => [a] -> [a] -> ([a], [a])
- splitOn :: Eq a => [a] -> [a] -> [[a]]
- split :: (a -> Bool) -> [a] -> [[a]]
- chunksOf :: Int -> [a] -> [[a]]
- list :: b -> (a -> [a] -> b) -> [a] -> b
- uncons :: [a] -> Maybe (a, [a])
- unsnoc :: [a] -> Maybe ([a], a)
- cons :: a -> [a] -> [a]
- snoc :: [a] -> a -> [a]
- drop1 :: [a] -> [a]
- mconcatMap :: Monoid b => (a -> b) -> [a] -> b
- groupSort :: Ord k => [(k, v)] -> [(k, [v])]
- groupSortOn :: Ord b => (a -> b) -> [a] -> [[a]]
- groupSortBy :: (a -> a -> Ordering) -> [a] -> [[a]]
- nubOrd :: Ord a => [a] -> [a]
- nubOrdBy :: (a -> a -> Ordering) -> [a] -> [a]
- nubOrdOn :: Ord b => (a -> b) -> [a] -> [a]
- nubOn :: Eq b => (a -> b) -> [a] -> [a]
- groupOn :: Eq b => (a -> b) -> [a] -> [[a]]
- sortOn :: Ord b => (a -> b) -> [a] -> [a]
- disjoint :: Eq a => [a] -> [a] -> Bool
- allSame :: Eq a => [a] -> Bool
- anySame :: Eq a => [a] -> Bool
- repeatedly :: ([a] -> (b, [a])) -> [a] -> [b]
- for :: [a] -> (a -> b) -> [b]
- firstJust :: (a -> Maybe b) -> [a] -> Maybe b
- concatUnzip :: [([a], [b])] -> ([a], [b])
- concatUnzip3 :: [([a], [b], [c])] -> ([a], [b], [c])
- replace :: Eq a => [a] -> [a] -> [a] -> [a]
- merge :: Ord a => [a] -> [a] -> [a]
- mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
- first :: (a -> a') -> (a, b) -> (a', b)
- second :: (b -> b') -> (a, b) -> (a, b')
- (***) :: (a -> a') -> (b -> b') -> (a, b) -> (a', b')
- (&&&) :: (a -> b) -> (a -> c) -> a -> (b, c)
- dupe :: a -> (a, a)
- both :: (a -> b) -> (a, a) -> (b, b)
- fst3 :: (a, b, c) -> a
- snd3 :: (a, b, c) -> b
- thd3 :: (a, b, c) -> c
- typeRep :: Typeable k a => proxy a -> TypeRep
- data (k :~: a) b :: forall k. k -> k -> * where
- data Proxy k t :: forall k. k -> * = Proxy
- makeVersion :: [Int] -> Version
- readVersion :: String -> Version
- showDP :: RealFloat a => Int -> a -> String
- intToDouble :: Int -> Double
- intToFloat :: Int -> Float
- floatToDouble :: Float -> Double
- doubleToFloat :: Double -> Float
- withCurrentDirectory :: FilePath -> IO a -> IO a
- createDirectoryPrivate :: String -> IO ()
- listContents :: FilePath -> IO [FilePath]
- listFiles :: FilePath -> IO [FilePath]
- listFilesInside :: (FilePath -> IO Bool) -> FilePath -> IO [FilePath]
- listFilesRecursive :: FilePath -> IO [FilePath]
- getExecutablePath :: IO FilePath
- lookupEnv :: String -> IO (Maybe String)
- isWindows :: Bool
- isMac :: Bool
- captureOutput :: IO a -> IO (String, a)
- withBuffering :: Handle -> BufferMode -> IO a -> IO a
- readFileEncoding :: TextEncoding -> FilePath -> IO String
- readFileUTF8 :: FilePath -> IO String
- readFileBinary :: FilePath -> IO String
- readFile' :: FilePath -> IO String
- readFileEncoding' :: TextEncoding -> FilePath -> IO String
- readFileUTF8' :: FilePath -> IO String
- readFileBinary' :: FilePath -> IO String
- writeFileEncoding :: TextEncoding -> FilePath -> String -> IO ()
- writeFileUTF8 :: FilePath -> String -> IO ()
- writeFileBinary :: FilePath -> String -> IO ()
- withTempFile :: (FilePath -> IO a) -> IO a
- withTempDir :: (FilePath -> IO a) -> IO a
- newTempFile :: IO (FilePath, IO ())
- newTempDir :: IO (FilePath, IO ())
- fileEq :: FilePath -> FilePath -> IO Bool
- system_ :: String -> IO ()
- systemOutput :: String -> IO (ExitCode, String)
- systemOutput_ :: String -> IO String
- type Seconds = Double
- sleep :: Seconds -> IO ()
- timeout :: Seconds -> IO a -> IO (Maybe a)
- subtractTime :: UTCTime -> UTCTime -> Seconds
- showDuration :: Seconds -> String
- offsetTime :: IO (IO Seconds)
- offsetTimeIncrease :: IO (IO Seconds)
- duration :: IO a -> IO (Seconds, a)

# Control.Concurrent.Extra

Extra functions available in `Control.Concurrent.Extra`

.

getNumCapabilities :: IO Int #

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`

.

*Since: 4.4.0.0*

setNumCapabilities :: Int -> IO () #

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.

*Since: 4.5.0.0*

withNumCapabilities :: Int -> IO a -> IO a Source #

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.

forkFinally :: IO a -> (Either SomeException a -> IO ()) -> IO ThreadId #

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.

*Since: 4.6.0.0*

once :: IO a -> IO (IO a) Source #

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.

let x ||| y = do t1 <- onceFork x; t2 <- onceFork y; t1; t2 \(x :: IO Int) -> void (once x) == return () \(x :: IO Int) -> join (once x) == x \(x :: IO Int) -> (do y <- once x; y; y) == x \(x :: IO Int) -> (do y <- once x; y ||| y) == x

onceFork :: IO a -> IO (IO a) Source #

Like `once`

, but immediately starts running the computation on a background thread.

\(x :: IO Int) -> join (onceFork x) == x \(x :: IO Int) -> (do a <- onceFork x; a; a) == x

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.

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.

modifyVar :: Var a -> (a -> IO (a, b)) -> IO b Source #

Modify a `Var`

producing a new value and a return result.

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.

signalBarrier :: Barrier a -> a -> IO () Source #

Write a value into the Barrier, releasing anyone at `waitBarrier`

.
Any subsequent attempts to signal the `Barrier`

will throw an exception.

waitBarrier :: Barrier a -> IO a Source #

Wait until a barrier has been signaled with `signalBarrier`

.

waitBarrierMaybe :: Barrier a -> IO (Maybe a) Source #

A version of `waitBarrier`

that never blocks, returning `Nothing`

if the barrier has not yet been signaled.

# Control.Exception.Extra

Extra functions available in `Control.Exception.Extra`

.

retry :: Int -> IO a -> IO a Source #

Retry an operation at most *n* times (*n* must be positive).
If the operation fails the *n*th time it will throw that final exception.

retry 1 (print "x") == print "x" retry 3 (fail "die") == fail "die"

retryBool :: Exception e => (e -> Bool) -> Int -> IO a -> IO a Source #

Retry an operation at most *n* times (*n* must be positive), while the exception value and type match a predicate.
If the operation fails the *n*th time it will throw that final exception.

showException :: Show e => e -> IO String Source #

Show a value, but if the result contains exceptions, produce
`<Exception>`

. Defined as

.
Particularly useful for printing exceptions to users, remembering that exceptions
can themselves contain undefined values.`stringException`

. show

stringException :: String -> IO String Source #

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>"

errorIO :: String -> IO a Source #

Like error, but in the `IO`

monad.
Note that while `fail`

in `IO`

raises an `IOException`

, this function raises an `ErrorCall`

exception.

try (errorIO "Hello") == return (Left (ErrorCall "Hello"))

displayException :: Exception e => e -> String #

ignore :: IO () -> IO () Source #

Ignore any exceptions thrown by the action.

ignore (print 1) == print 1 ignore (fail "die") == return ()

catch_ :: IO a -> (SomeException -> IO a) -> IO a Source #

A version of `catch`

without the `Exception`

context, restricted to `SomeException`

,
so catches all exceptions.

catchJust_ :: (SomeException -> Maybe b) -> IO a -> (b -> IO a) -> IO a Source #

handleJust_ :: (SomeException -> Maybe b) -> (b -> IO a) -> IO a -> IO a Source #

Like `catch_`

but for `handleJust`

catchBool :: Exception e => (e -> Bool) -> IO a -> (e -> IO a) -> IO a Source #

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 "")

# Control.Monad.Extra

Extra functions available in `Control.Monad.Extra`

.

whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m () Source #

whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m () Source #

Like `whenJust`

, but where the test can be monadic.

The identity function which requires the inner argument to be `()`

. Useful for functions
with overloaded return types.

\(x :: Maybe ()) -> unit x == x

maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b Source #

Monadic generalisation of `maybe`

.

eitherM :: Monad m => (a -> m c) -> (b -> m c) -> m (Either a b) -> m c Source #

Monadic generalisation of `either`

.

partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a]) Source #

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

concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] Source #

A version of `concatMap`

that works with a monadic predicate.

concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b] Source #

Like `concatMapM`

, but has its arguments flipped, so can be used
instead of the common `fmap concat $ forM`

pattern.

mconcatMapM :: (Monad m, Monoid b) => (a -> m b) -> [a] -> m b Source #

A version of `mconcatMap`

that works with a monadic predicate.

mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b] Source #

A version of `mapMaybe`

that works with a monadic predicate.

findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a) Source #

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")

firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b) Source #

Like `findM`

, but also allows you to compute some additional information in the predicate.

unlessM :: Monad m => m Bool -> m () -> m () Source #

Like `unless`

, but where the test can be monadic.

orM :: Monad m => [m Bool] -> m Bool Source #

A version of `or`

lifted to a monad. 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)

andM :: Monad m => [m Bool] -> m Bool Source #

A version of `and`

lifted to a monad. 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)

anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool Source #

A version of `any`

lifted to a monad. 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)

allM :: Monad m => (a -> m Bool) -> [a] -> m Bool Source #

A version of `all`

lifted to a monad. 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)

# Data.Either.Extra

Extra functions available in `Data.Either.Extra`

.

isLeft :: Either a b -> Bool #

Return `True`

if the given value is a `Left`

-value, `False`

otherwise.

#### Examples

Basic usage:

`>>>`

True`isLeft (Left "foo")`

`>>>`

False`isLeft (Right 3)`

Assuming a `Left`

value signifies some sort of error, we can use
`isLeft`

to write a very simple error-reporting function that does
absolutely nothing in the case of success, and outputs "ERROR" if
any error occurred.

This example shows how `isLeft`

might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:

`>>>`

`import Control.Monad ( when )`

`>>>`

`let report e = when (isLeft e) $ putStrLn "ERROR"`

`>>>`

`report (Right 1)`

`>>>`

ERROR`report (Left "parse error")`

*Since: 4.7.0.0*

isRight :: Either a b -> Bool #

Return `True`

if the given value is a `Right`

-value, `False`

otherwise.

#### Examples

Basic usage:

`>>>`

False`isRight (Left "foo")`

`>>>`

True`isRight (Right 3)`

Assuming a `Left`

value signifies some sort of error, we can use
`isRight`

to write a very simple reporting function that only
outputs "SUCCESS" when a computation has succeeded.

This example shows how `isRight`

might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:

`>>>`

`import Control.Monad ( when )`

`>>>`

`let report e = when (isRight e) $ putStrLn "SUCCESS"`

`>>>`

`report (Left "parse error")`

`>>>`

SUCCESS`report (Right 1)`

*Since: 4.7.0.0*

fromEither :: Either a a -> a Source #

Pull the value out of an `Either`

where both alternatives
have the same type.

\x -> fromEither (Left x ) == x \x -> fromEither (Right x) == x

# Data.IORef.Extra

Extra functions available in `Data.IORef.Extra`

.

modifyIORef' :: IORef a -> (a -> a) -> IO () #

Strict version of `modifyIORef`

*Since: 4.6.0.0*

writeIORef' :: IORef a -> a -> IO () Source #

Evaluates the value before calling `writeIORef`

.

atomicModifyIORef' :: IORef a -> (a -> (a, b)) -> IO b #

Strict version of `atomicModifyIORef`

. This forces both the value stored
in the `IORef`

as well as the value returned.

*Since: 4.6.0.0*

atomicWriteIORef :: IORef a -> a -> IO () #

Variant of `writeIORef`

with the "barrier to reordering" property that
`atomicModifyIORef`

has.

*Since: 4.6.0.0*

atomicWriteIORef' :: IORef a -> a -> IO () Source #

Evaluates the value before calling `atomicWriteIORef`

.

# Data.List.Extra

Extra functions available in `Data.List.Extra`

.

lower :: String -> String Source #

Convert a string to lower case.

lower "This is A TEST" == "this is a test" lower "" == ""

upper :: String -> String Source #

Convert a string to upper case.

upper "This is A TEST" == "THIS IS A TEST" upper "" == ""

word1 :: String -> (String, String) Source #

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)

line1 :: String -> (String, String) Source #

Split the first line off a string.

line1 "" == ("", "") line1 "test" == ("test","") line1 "test\n" == ("test","") line1 "test\nrest" == ("test","rest") line1 "test\nrest\nmore" == ("test","rest\nmore")

dropEnd :: Int -> [a] -> [a] Source #

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..]

takeEnd :: Int -> [a] -> [a] Source #

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)

splitAtEnd :: Int -> [a] -> ([a], [a]) Source #

returns a split where the second element tries to
contain `splitAtEnd`

n xs`n`

elements.

splitAtEnd 3 "hello" == ("he","llo") splitAtEnd 3 "he" == ("", "he") \i xs -> uncurry (++) (splitAt i xs) == xs \i xs -> splitAtEnd i xs == (dropEnd i xs, takeEnd i xs)

breakEnd :: (a -> Bool) -> [a] -> ([a], [a]) Source #

Break, but from the end.

breakEnd isLower "youRE" == ("you","RE") breakEnd isLower "youre" == ("youre","") breakEnd isLower "YOURE" == ("","YOURE") \f xs -> breakEnd (not . f) xs == spanEnd f xs

spanEnd :: (a -> Bool) -> [a] -> ([a], [a]) Source #

Span, but from the end.

spanEnd isUpper "youRE" == ("you","RE") spanEnd (not . isSpace) "x y z" == ("x y ","z") \f xs -> uncurry (++) (spanEnd f xs) == xs \f xs -> spanEnd f xs == swap (both reverse (span f (reverse xs)))

dropWhileEnd :: (a -> Bool) -> [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

*Since: 4.5.0.0*

dropWhileEnd' :: (a -> Bool) -> [a] -> [a] Source #

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

takeWhileEnd :: (a -> Bool) -> [a] -> [a] Source #

A version of `takeWhile`

operating from the end.

takeWhileEnd even [2,3,4,6] == [4,6]

stripSuffix :: Eq a => [a] -> [a] -> Maybe [a] Source #

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

stripInfix :: Eq a => [a] -> [a] -> Maybe ([a], [a]) Source #

Return the the string before and after the search string,
or `Nothing`

if the search string is not present.

Examples:

stripInfix "::" "a::b::c" == Just ("a", "b::c") stripInfix "/" "foobar" == Nothing

stripInfixEnd :: Eq a => [a] -> [a] -> Maybe ([a], [a]) Source #

Similar to `stripInfix`

, but searches from the end of the
string.

stripInfixEnd "::" "a::b::c" == Just ("a::b", "c")

wordsBy :: (a -> Bool) -> [a] -> [[a]] Source #

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

linesBy :: (a -> Bool) -> [a] -> [[a]] Source #

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"]

breakOn :: Eq a => [a] -> [a] -> ([a], [a]) Source #

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.
If you want the remainder *without* the patch, use `stripInfix`

.

breakOn "::" "a::b::c" == ("a", "::b::c") breakOn "/" "foobar" == ("foobar", "") \needle haystack -> let (prefix,match) = breakOn needle haystack in prefix ++ match == haystack

breakOnEnd :: Eq a => [a] -> [a] -> ([a], [a]) Source #

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")

splitOn :: Eq a => [a] -> [a] -> [[a]] Source #

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

split :: (a -> Bool) -> [a] -> [[a]] Source #

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"]

chunksOf :: Int -> [a] -> [[a]] Source #

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

list :: b -> (a -> [a] -> b) -> [a] -> b Source #

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

cons :: a -> [a] -> [a] Source #

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)

snoc :: [a] -> a -> [a] Source #

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)

Equivalent to `drop 1`

, but likely to be faster and a single lexeme.

drop1 "" == "" drop1 "test" == "est" \xs -> drop 1 xs == drop1 xs

mconcatMap :: Monoid b => (a -> b) -> [a] -> b Source #

groupSortOn :: Ord b => (a -> b) -> [a] -> [[a]] Source #

groupSortBy :: (a -> a -> Ordering) -> [a] -> [[a]] Source #

nubOrd :: Ord a => [a] -> [a] Source #

*O(n log n)*. The `nubOrd`

function removes duplicate elements from a list.
In particular, it keeps only the first occurrence of each element.
Unlike the standard `nub`

operator, this version requires an `Ord`

instance
and consequently runs asymptotically faster.

nubOrd "this is a test" == "this ae" nubOrd (take 4 ("this" ++ undefined)) == "this" \xs -> nubOrd xs == nub xs

nubOrdBy :: (a -> a -> Ordering) -> [a] -> [a] Source #

A version of `nubOrd`

with a custom predicate.

nubOrdBy (compare `on` length) ["a","test","of","this"] == ["a","test","of"]

nubOrdOn :: Ord b => (a -> b) -> [a] -> [a] Source #

A version of `nubOrd`

which operates on a portion of the value.

nubOrdOn length ["a","test","of","this"] == ["a","test","of"]

groupOn :: Eq b => (a -> b) -> [a] -> [[a]] Source #

A version of `group`

where the equality is done on some extracted value.

sortOn :: Ord 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.

*Since: 4.8.0.0*

disjoint :: Eq a => [a] -> [a] -> Bool Source #

Are two lists disjoint, with no elements in common.

disjoint [1,2,3] [4,5] == True disjoint [1,2,3] [4,1] == False

allSame :: Eq a => [a] -> Bool Source #

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)

anySame :: Eq a => [a] -> Bool Source #

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)

repeatedly :: ([a] -> (b, [a])) -> [a] -> [b] Source #

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 \xs -> repeatedly line1 xs == lines xs

firstJust :: (a -> Maybe b) -> [a] -> Maybe b Source #

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

concatUnzip :: [([a], [b])] -> ([a], [b]) Source #

concatUnzip3 :: [([a], [b], [c])] -> ([a], [b], [c]) Source #

replace :: Eq a => [a] -> [a] -> [a] -> [a] Source #

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

merge :: Ord a => [a] -> [a] -> [a] Source #

Merge two lists which are assumed to be ordered.

merge "ace" "bd" == "abcde" \xs ys -> merge (sort xs) (sort ys) == sort (xs ++ ys)

mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a] Source #

Like `merge`

, but with a custom ordering function.

# Data.Tuple.Extra

Extra functions available in `Data.Tuple.Extra`

.

first :: (a -> a') -> (a, b) -> (a', b) Source #

Update the first component of a pair.

first succ (1,"test") == (2,"test")

second :: (b -> b') -> (a, b) -> (a, b') Source #

Update the second component of a pair.

second reverse (1,"test") == (1,"tset")

(***) :: (a -> a') -> (b -> b') -> (a, b) -> (a', b') infixr 3 Source #

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 -> b) -> (a -> c) -> a -> (b, c) infixr 3 Source #

Given two functions, apply both to a single argument to form a pair.
A specialised version of `&&&`

.

(succ &&& pred) 1 == (2,0)

both :: (a -> b) -> (a, a) -> (b, b) Source #

Apply a single function to both components of a pair.

both succ (1,2) == (2,3)

# Data.Typeable.Extra

Extra functions available in `Data.Typeable.Extra`

.

typeRep :: Typeable k a => proxy a -> TypeRep #

Takes a value of type `a`

and returns a concrete representation
of that type.

*Since: 4.7.0.0*

data (k :~: a) b :: forall k. k -> k -> * where infix 4 #

Propositional equality. If `a :~: b`

is inhabited by some terminating
value, then the type `a`

is the same as the type `b`

. To use this equality
in practice, pattern-match on the `a :~: b`

to get out the `Refl`

constructor;
in the body of the pattern-match, the compiler knows that `a ~ b`

.

*Since: 4.7.0.0*

data Proxy k t :: forall k. k -> * #

A concrete, poly-kinded proxy type

Monad (Proxy *) | |

Functor (Proxy *) | |

Applicative (Proxy *) | |

Foldable (Proxy *) | |

Traversable (Proxy *) | |

Generic1 (Proxy *) | |

Alternative (Proxy *) | |

MonadPlus (Proxy *) | |

Bounded (Proxy k s) | |

Enum (Proxy k s) | |

Eq (Proxy k s) | |

Ord (Proxy k s) | |

Read (Proxy k s) | |

Show (Proxy k s) | |

Ix (Proxy k s) | |

Generic (Proxy k t) | |

Semigroup (Proxy k s) | |

Monoid (Proxy k s) | |

type Rep1 (Proxy *) | |

type Rep (Proxy k t) | |

# Data.Version.Extra

Extra functions available in `Data.Version.Extra`

.

makeVersion :: [Int] -> Version #

Construct tag-less `Version`

*Since: 4.8.0.0*

readVersion :: String -> Version Source #

Read a `Version`

or throw an exception.

\x -> readVersion (showVersion x) == x readVersion "hello" == undefined

# Numeric.Extra

Extra functions available in `Numeric.Extra`

.

showDP :: RealFloat a => Int -> a -> String Source #

Show a number to a fixed number of decimal places.

showDP 4 pi == "3.1416" showDP 0 pi == "3" showDP 2 3 == "3.00"

intToDouble :: Int -> Double Source #

Specialised numeric conversion, type restricted version of `fromIntegral`

.

intToFloat :: Int -> Float Source #

Specialised numeric conversion, type restricted version of `fromIntegral`

.

floatToDouble :: Float -> Double Source #

Specialised numeric conversion, type restricted version of `realToFrac`

.

doubleToFloat :: Double -> Float Source #

Specialised numeric conversion, type restricted version of `realToFrac`

.

# System.Directory.Extra

Extra functions available in `System.Directory.Extra`

.

Run an `IO`

action with the given working directory and restore the
original working directory afterwards, even if the given action fails due
to an exception.

The operation may fail with the same exceptions as `getCurrentDirectory`

and `setCurrentDirectory`

.

*Since: 1.2.3.0*

createDirectoryPrivate :: String -> IO () Source #

Create a directory with permissions so that only the current user can view it.
On Windows this function is equivalent to `createDirectory`

.

listContents :: FilePath -> IO [FilePath] Source #

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"]

listFiles :: FilePath -> IO [FilePath] Source #

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"]

listFilesInside :: (FilePath -> IO Bool) -> FilePath -> IO [FilePath] Source #

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"] []

listFilesRecursive :: FilePath -> IO [FilePath] Source #

Like `listFiles`

, but goes recursively through all subdirectories.

listTest listFilesRecursive ["bar.txt","zoo","foo" </> "baz.txt"] ["bar.txt","zoo","foo" </> "baz.txt"]

# System.Environment.Extra

Extra functions available in `System.Environment.Extra`

.

getExecutablePath :: 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.)

*Since: 4.6.0.0*

lookupEnv :: String -> IO (Maybe String) #

Return the value of the environment variable `var`

, or `Nothing`

if
there is no such value.

For POSIX users, this is equivalent to `getEnv`

.

*Since: 4.6.0.0*

# System.Info.Extra

Extra functions available in `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")

# System.IO.Extra

Extra functions available in `System.IO.Extra`

.

withBuffering :: Handle -> BufferMode -> IO a -> IO a Source #

Execute an action with a custom `BufferMode`

, a wrapper around
`hSetBuffering`

.

readFileEncoding :: TextEncoding -> FilePath -> IO String Source #

Like `readFile`

, but setting an encoding.

readFile' :: FilePath -> IO String Source #

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.

\(filter isHexDigit -> s) -> fmap (== s) $ withTempFile $ \file -> do writeFile file s; readFile' file

readFileEncoding' :: TextEncoding -> FilePath -> IO String Source #

A strict version of `readFileEncoding`

, see `readFile'`

for details.

readFileUTF8' :: FilePath -> IO String Source #

A strict version of `readFileUTF8`

, see `readFile'`

for details.

readFileBinary' :: FilePath -> IO String Source #

A strict version of `readFileBinary`

, see `readFile'`

for details.

writeFileEncoding :: TextEncoding -> FilePath -> String -> IO () Source #

Write a file with a particular encoding.

writeFileUTF8 :: FilePath -> String -> IO () Source #

Write a file with the `utf8`

encoding.

\s -> withTempFile $ \file -> do writeFileUTF8 file s; fmap (== s) $ readFileUTF8' file

writeFileBinary :: FilePath -> String -> IO () Source #

Write a binary file.

\s -> withTempFile $ \file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file

withTempFile :: (FilePath -> IO a) -> IO a Source #

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 ""

withTempDir :: (FilePath -> IO a) -> IO a Source #

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 []

newTempFile :: IO (FilePath, IO ()) Source #

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.

newTempDir :: IO (FilePath, IO ()) Source #

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.

fileEq :: FilePath -> FilePath -> IO Bool Source #

Returns `True`

if both files have the same content.
Raises an error if either file is missing.

fileEq "does_not_exist1" "does_not_exist2" == undefined fileEq "does_not_exist" "does_not_exist" == undefined withTempFile $ \f1 -> fileEq "does_not_exist" f1 == undefined withTempFile $ \f1 -> withTempFile $ \f2 -> fileEq f1 f2 withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "a" >> fileEq f1 f2 withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "b" >> notM (fileEq f1 f2)

# System.Process.Extra

Extra functions available in `System.Process.Extra`

.

system_ :: String -> IO () Source #

A version of `system`

that throws an error if the `ExitCode`

is not `ExitSuccess`

.

systemOutput_ :: String -> IO String Source #

A version of `system`

that captures the output (both `stdout`

and `stderr`

)
and throws an error if the `ExitCode`

is not `ExitSuccess`

.

# System.Time.Extra

Extra functions available in `System.Time.Extra`

.

sleep :: Seconds -> IO () Source #

Sleep for a number of seconds.

fmap (round . fst) (duration $ sleep 1) == return 1

timeout :: Seconds -> IO a -> IO (Maybe a) Source #

A version of `timeout`

that takes `Seconds`

and never
overflows the bounds of an `Int`

. In addition, the bug that negative
timeouts run for ever has been fixed.

timeout (-3) (print 1) == return Nothing timeout 0.1 (print 1) == fmap Just (print 1) do (t, _) <- duration $ timeout 0.1 $ sleep 1000; print t; return $ t < 1 timeout 0.1 (sleep 2 >> print 1) == return Nothing

subtractTime :: UTCTime -> UTCTime -> Seconds Source #

Deprecated: Function is being retired - use diffUTCTime directly.

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.

showDuration :: Seconds -> String Source #

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"

offsetTime :: IO (IO Seconds) Source #

Call once to start, then call repeatedly to get the elapsed time since the first call. The time is guaranteed to be monotonic. This function is robust to system time changes.

do f <- offsetTime; xs <- replicateM 10 f; return $ xs == sort xs

offsetTimeIncrease :: IO (IO Seconds) Source #

Deprecated: Use offsetTime instead, which is guaranteed to always increase.

A synonym for `offsetTime`

.