IO package:haskeline

This module provides a stateful, IO-based interface to Haskeline, which may be easier to integrate into some existing programs or libraries. It is strongly recommended to use the safer, monadic API of System.Console.Haskeline, if possible, rather than the explicit state management functions of this module. The equivalent REPL example is:

import System.Console.Haskeline
import System.Console.Haskeline.IO
import Control.Concurrent

main = bracketOnError (initializeInput defaultSettings)
cancelInput -- This will only be called if an exception such
-- as a SigINT is received.
(\hd -> loop hd >> closeInput hd)
where
loop :: InputState -> IO ()
loop hd = do
minput <- queryInput hd (getInputLine "% ")
case minput of
Nothing -> return ()
Just "quit" -> return ()
Just input -> do queryInput hd $ outputStrLn
$ "Input was: " ++ input
loop hd

Haskeline has two ways of interacting with the user:

• "Terminal-style" interaction provides an rich user interface by connecting to the user's terminal (which may be different than stdin or stdout).
• "File-style" interaction treats the input as a simple stream of characters, for example when reading from a file or pipe. Input functions (e.g., getInputLine) print the prompt to stdout.

A Behavior is a method for deciding at run-time which type of interaction to use. For most applications (e.g., a REPL), defaultBehavior should have the correct effect.

Read input from stdin. Use terminal-style interaction if stdin is connected to a terminal and has echoing enabled. Otherwise (e.g., if stdin is a pipe), use file-style interaction. This behavior should suffice for most applications.

Run a line-reading application according to the given behavior. If it uses terminal-style interaction, Prefs will be read from the user's ~/.haskeline file (if present). If it uses file-style interaction, Prefs are not relevant and will not be read.

Run a line-reading application.

Performs completions from the given line state. The first String argument is the contents of the line to the left of the cursor, reversed. The second String argument is the contents of the line to the right of the cursor. The output String is the unused portion of the left half of the line, reversed.

If the first completer produces no suggestions, fallback to the second completer's output.

Disable completion altogether.

Create a finished completion out of the given word.