Module "IOExts.curry"

Library with some useful extensions to the IO monad.

Author: Michael Hanus

Version: June 2007

Exported names:

Datatypes:
IORef

Summary of exported functions:

execCmd :: String -> IO (Handle,Handle,Handle)

Executes a command with a new default shell process.

connectToCommand :: String -> IO Handle

Executes a command with a new default shell process.

readCompleteFile :: String -> IO String

An action that reads the complete contents of a file and returns it.

updateFile :: (String -> String) -> String -> IO ()

An action that updates the contents of a file.

exclusiveIO :: String -> IO a -> IO a

Forces the exclusive execution of an action via a lock file.

setAssoc :: String -> String -> IO ()

Defines a global association between two strings.

getAssoc :: String -> IO (Maybe String)

Gets the value associated to a string.

newIORef :: a -> IO (IORef a)

Creates a new IORef with an initial values.

readIORef :: IORef a -> IO a

Reads the current value of an IORef.

writeIORef :: IORef a -> a -> IO ()

Updates the value of an IORef.

Imported modules:

IO
Prelude
System

Exported datatypes:

IORef

Mutable variables containing values of some type. The values are not evaluated when they are assigned to an IORef.

Constructors:

Exported functions:

execCmd :: String -> IO (Handle,Handle,Handle)

Executes a command with a new default shell process. The standard I/O streams of the new process (stdin,stdout,stderr) are returned as handles so that they can be explicitly manipulated. They should be closed with IO.hClose since they are not closed automatically when the process terminates.

Example call: (execCmd cmd)

Parameters:
: cmd - the shell command to be executed

Returns:: the handles of the input/output/error streams of the new process

connectToCommand :: String -> IO Handle

Executes a command with a new default shell process. The input and output streams of the new process is returned as one handle which is both readable and writable. Thus, writing to the handle produces input to the process and output from the process can be retrieved by reading from this handle. The handle should be closed with IO.hClose since they are not closed automatically when the process terminates.

Example call: (connectToCommand cmd)

Parameters:
: cmd - the shell command to be executed

Returns:: the handle connected to the input/output streams of the new process

readCompleteFile :: String -> IO String

An action that reads the complete contents of a file and returns it. This action can be used instead of the (lazy) readFile action if the contents of the file might be changed.

Example call: (readCompleteFile file)

Parameters:
: file - the name of the file

Returns:: the complete contents of the file

updateFile :: (String -> String) -> String -> IO ()

An action that updates the contents of a file.

Example call: (updateFile f file)

Parameters:
: f - the function to transform the contents
: file - the name of the file

exclusiveIO :: String -> IO a -> IO a

Forces the exclusive execution of an action via a lock file. For instance, (exclusiveIO "myaction.lock" act) ensures that the action "act" is not executed by two processes on the same system at the same time.

Example call: (exclusiveIO lockfile action)

Parameters:
: lockfile - the name of a global lock file
: action - the action to be exclusively executed

Returns:: the result of the execution of the action

setAssoc :: String -> String -> IO ()

Defines a global association between two strings. Both arguments must be evaluable to ground terms before applying this operation.