A rich user interface for line input in command-line programs. Haskeline is Unicode-aware and runs both on POSIX-compatible systems and on Windows.

Users may customize the interface with a ~/.haskeline file; see http://trac.haskell.org/haskeline/wiki/UserPrefs for more information.

An example use of this library for a simple read-eval-print loop is the following:

 import System.Console.Haskeline
 
 main :: IO ()
 main = runInputT defaultSettings loop
    where 
        loop :: InputT IO ()
        loop = do
            minput <- getInputLine "% "
            case minput of
                Nothing -> return ()
                Just "quit" -> return ()
                Just input -> do outputStrLn $ "Input was: " ++ input
                                 loop

The following functions read one line or character of input from the user.

If stdin is connected to a terminal, then these functions perform all user interaction, including display of the prompt text, on the user's output terminal (which may differ from stdout). They return Nothing if the user pressed Ctrl-D when the input text was empty.

If stdin is not connected to a terminal or does not have echoing enabled, then these functions print the prompt to stdout, and they return Nothing if an EOF was encountered before any characters were read.

A useful default. In particular:

 defaultSettings = Settings {
           complete = completeFilename,
           historyFile = Nothing,
           autoAddHistory = True
           }

The following functions provide portable handling of Ctrl-C events.

These functions are not necessary on GHC version 6.10 or later, which processes Ctrl-C events as exceptions by default.