extra-1.6.14: Extra functions I use.

Extra

Description

Deprecated: This module is provided as documentation of all new functions, you should import the more specific modules directly.

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).

Synopsis

# Control.Concurrent.Extra

Extra functions available in 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.

Since: base-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: base-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: base-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

data Lock Source #

Like an MVar, but has no value. Used to guarantee 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.

Create a new Lock.

withLock :: Lock -> IO a -> IO a Source #

Perform some operation while holding Lock. Will prevent all other operations from using the Lock while the action is ongoing.

withLockTry :: Lock -> IO a -> IO (Maybe a) Source #

Like withLock but will never block. If the operation cannot be executed immediately it will return Nothing.

data Var a Source #

Like an MVar, but must always be full. Used to operate on a mutable variable in a thread-safe way. As an example:

hits <- newVar 0
forkIO $do ...; modifyVar_ hits (+1); ... i <- readVar hits print ("HITS",i)  Here we have a variable which we modify atomically, so modifications are not interleaved. This use of MVar never blocks on a put. No modifyVar operation should ever block, and they should always complete in a reasonable timeframe. A Var should not be used to protect some external resource, only the variable contained within. Information from a readVar should not be subsequently inserted back into the Var. newVar :: a -> IO (Var a) Source # Create a new Var with a value. readVar :: Var a -> IO a Source # Read the current value of the Var. writeVar :: Var a -> a -> IO () Source # Write a value to become the new value of Var. modifyVar :: Var a -> (a -> IO (a, b)) -> IO b Source # Modify a Var producing a new value and a return result. modifyVar_ :: Var a -> (a -> IO a) -> IO () Source # Modify a Var, a restricted version of modifyVar. withVar :: Var a -> (a -> IO b) -> IO b Source # Perform some operation using the value in the Var, a restricted version of modifyVar. data Barrier a Source # Starts out empty, then is filled exactly once. As an example: bar <- newBarrier forkIO$ 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.

Create a new Barrier.

signalBarrier :: Partial => 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.

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.

A constraint which documents that a function is partial, and on GHC 8.0 and above produces a stack trace on failure. For example:

myHead :: Partial => [a] -> a
myHead (x:xs) = x


When using Partial with GHC 7.8 or below you need to enable the language feature ConstraintKinds, e.g. {-# LANGUAGE ConstraintKinds #-} at the top of the file.

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

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"

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 nth time it will throw that final exception.

errorWithoutStackTrace :: [Char] -> a #

A variant of error that does not produce a stack trace.

Since: base-4.9.0.0

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

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.

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>"

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 #

Render this exception value in a human-friendly manner.

Default implementation: show.

Since: base-4.8.0.0

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.

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

Like catch_ but for handle

try_ :: IO a -> IO (Either SomeException a) Source #

Like catch_ but for try

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

Like catch_ but for catchJust

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

Like catch_ but for handleJust

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

Like catch_ but for tryJust

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 "")  handleBool :: Exception e => (e -> Bool) -> (e -> IO a) -> IO a -> IO a Source # Like catchBool but for handle. tryBool :: Exception e => (e -> Bool) -> IO a -> IO (Either e a) Source # Like catchBool but for try. # Control.Monad.Extra Extra functions available in Control.Monad.Extra. whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m () Source # Perform some operation on Just, given the field inside the Just. whenJust Nothing print == return () whenJust (Just 1) print == print 1 whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m () Source # Like whenJust, but where the test can be monadic. whenMaybe :: Applicative m => Bool -> m a -> m (Maybe a) Source # Like when, but return either Nothing if the predicate was False, of Just with the result of the computation. whenMaybe True (print 1) == fmap Just (print 1) whenMaybe False (print 1) == return Nothing whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a) Source # Like whenMaybe, but where the test can be monadic. unit :: m () -> m () Source # 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. loop :: (a -> Either a b) -> a -> b Source # A looping operation, where the predicate returns Left as a seed for the next loop or Right to abort the loop. loop (\x -> if x < 10 then Left$ x * 2 else Right $show x) 1 == "16" loopM :: Monad m => (a -> m (Either a b)) -> a -> m b Source # A monadic version of loop, where the predicate returns Left as a seed for the next loop or Right to abort the loop. whileM :: Monad m => m Bool -> m () Source # Keep running an operation until it becomes False. As an example: whileM$ do sleep 0.1; notM $doesFileExist "foo.txt" readFile "foo.txt"  If you need some state persisted between each test, use loopM. partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a]) Source # A version of partition that works with a monadic predicate. partitionM (Just . even) [1,2,3] == Just ([2], [1,3]) partitionM (const Nothing) [1,2,3] == Nothing concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] Source # A version of concatMap that works with a monadic predicate. concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b] Source # Like concatMapM, but has its arguments flipped, so can be used instead of the common fmap concat$ 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.

fold1M :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m a Source #

A variant of foldM that has no base case, and thus may only be applied to non-empty lists.

fold1M (\x y -> Just x) [] == undefined
fold1M (\x y -> Just $x + y) [1, 2, 3] == Just 6 fold1M_ :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m () Source # Like fold1M but discards the result. whenM :: Monad m => m Bool -> m () -> m () Source # Like when, but where the test can be monadic. unlessM :: Monad m => m Bool -> m () -> m () Source # Like unless, but where the test can be monadic. ifM :: Monad m => m Bool -> m a -> m a -> m a Source # Like if, but where the test can be monadic. notM :: Functor m => m Bool -> m Bool Source # Like not, but where the test can be monadic. (||^) :: Monad m => m Bool -> m Bool -> m Bool Source # 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 Source # 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 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 Expand Basic usage: >>> isLeft (Left "foo") True >>> isLeft (Right 3) False  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)
>>> report (Left "parse error")
ERROR


Since: base-4.7.0.0

isRight :: Either a b -> Bool #

Return True if the given value is a Right-value, False otherwise.

#### Examples

Expand

Basic usage:

>>> isRight (Left "foo")
False
>>> isRight (Right 3)
True


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 )

# Data.Version.Extra

Extra functions available in Data.Version.Extra.

makeVersion :: [Int] -> Version #

Construct tag-less Version

Since: base-4.8.0.0

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"

Specialised numeric conversion, type restricted version of fromIntegral.

Specialised numeric conversion, type restricted version of fromIntegral.

Specialised numeric conversion, type restricted version of realToFrac.

Specialised numeric conversion, type restricted version of realToFrac.

# System.Directory.Extra

Extra functions available in System.Directory.Extra.

Arguments

 :: FilePath Directory to execute in -> IO a Action to be executed -> IO a

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: directory-1.2.3.0

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

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"]

Like listContents, but only returns the directories in a directory, not the files. Each directory will be prefixed by the query directory.

listTest listDirectories ["bar.txt","foo/baz.txt","zoo"] ["foo"]

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"] [] Like listFiles, but goes recursively through all subdirectories. This function will follow symlinks, and if they form a loop, this function will not terminate. listTest listFilesRecursive ["bar.txt","zoo","foo" </> "baz.txt"] ["bar.txt","zoo","foo" </> "baz.txt"] # System.Environment.Extra Extra functions available in 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.) Since base 4.11.0.0, getExecutablePath resolves symlinks on Windows. If an executable is launched through a symlink, getExecutablePath returns the absolute path of the original executable. Since: base-4.6.0.0 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: base-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") Return True on Mac OS X and False otherwise. # System.IO.Extra Extra functions available in System.IO.Extra. captureOutput :: IO a -> IO (String, a) Source # Capture the stdout and stderr of a computation. captureOutput (print 1) == return ("1\n",()) withBuffering :: Handle -> BufferMode -> IO a -> IO a Source # Execute an action with a custom BufferMode, a wrapper around hSetBuffering. Like readFile, but setting an encoding. Like readFile, but with the encoding utf8. Like readFile, but for binary files. 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 $\file -> do writeFile file s; readFile' file A strict version of readFileEncoding, see readFile' for details. A strict version of readFileUTF8, see readFile' for details. A strict version of readFileBinary, see readFile' for details. Write a file with a particular encoding. Write a file with the utf8 encoding. \s -> withTempFile$ \file -> do writeFileUTF8 file s; fmap (== s) $readFileUTF8' file Write a binary file. \(ASCIIString s) -> withTempFile$ \file -> do writeFileBinary file s; fmap (== s) $readFileBinary' file withTempFile :: (FilePath -> IO a) -> IO a Source # Create a temporary file in the temporary directory. The file will be deleted after the action completes (provided the file is not still open). The FilePath will not have any file extension, will exist, and will be zero bytes long. If you require a file with a specific name, use withTempDir. withTempFile doesFileExist == return True (doesFileExist =<< withTempFile return) == return False withTempFile readFile' == return "" withTempDir :: (FilePath -> IO a) -> IO a Source # Create a temporary directory inside the system temporary directory. The directory will be deleted after the action completes. withTempDir doesDirectoryExist == return True (doesDirectoryExist =<< withTempDir return) == return False withTempDir listFiles == return [] Provide a function to create a temporary file, and a way to delete a temporary file. Most users should use withTempFile which combines these operations. Provide a function to create a temporary directory, and a way to delete a temporary directory. Most users should use withTempDir which combines these operations. Like newTempFile but using a custom temporary directory. Like newTempDir but using a custom temporary directory. Returns True if both files have the same content. Raises an error if either file is missing. fileEq "does_not_exist1" "does_not_exist2" == undefined fileEq "does_not_exist" "does_not_exist" == undefined withTempFile$ \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_ :: Partial => String -> IO () Source #

A version of system that throws an error if the ExitCode is not ExitSuccess.

A version of system that also captures the output, both stdout and stderr. Returns a pair of the ExitCode and the output.

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.

type Seconds = Double Source #

A type alias for seconds, which are stored as Double.

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

Show a number of seconds, typically a duration, in a suitable manner with reasonable precision for a human.

showDuration 3.435   == "3.44s"
showDuration 623.8   == "10m24s"
showDuration 62003.8 == "17h13m"
showDuration 1e8     == "27777h47m"

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 $xs == sort xs Deprecated: Use offsetTime instead, which is guaranteed to always increase. A synonym for offsetTime. duration :: IO a -> IO (Seconds, a) Source # Record how long a computation takes in Seconds. do (a,_) <- duration$ sleep 1; return \$ a >= 1 && a <= 1.5

Extra functions available in Text.Read.Extra.

readEither :: Read a => String -> Either String a #

Parse a string using the Read instance. Succeeds if there is exactly one valid result. A Left value indicates a parse error.

>>> readEither "123" :: Either String Int
Right 123

>>> readEither "hello" :: Either String Int
Left "Prelude.read: no parse"


Since: base-4.6.0.0

readMaybe :: Read a => String -> Maybe a #

Parse a string using the Read instance. Succeeds if there is exactly one valid result.

>>> readMaybe "123" :: Maybe Int
Just 123

>>> readMaybe "hello" :: Maybe Int
Nothing


Since: base-4.6.0.0