I'm writing a terminal-mode program in Haskell. How would I go about reading raw keypress information?
In particular, there seems to be something providing line-editing facilities on top of Haskell. If I do getLine, I seem to be able to use the up-arrow to get previous lines, edit the text, and only when I press Enter does the text become visible to the Haskell application itself.
What I'm after is the ability to read individual keypresses, so I can implement the line-editing stuff myself.
Perhaps my question was unclear. Basically I want to build something like Vi or Emacs (or Yi). I already know there are terminal bindings that will let me do fancy console-mode printing, so the output side shouldn't be an issue. I'm just looking for a way to get at raw keypress input, so I can do things like (for example) add K to the current line of text when the user presses the letter K, or save the file to disk when the user presses Ctrl+S.
Sounds like you want readline support. There are a couple of packages to do this, but haskeline is probably the easiest to use with the most supported platforms.
import Control.Monad.Trans
import System.Console.Haskeline
type Repl a = InputT IO a
process :: String -> IO ()
process = putStrLn
repl :: Repl ()
repl = do
minput <- getInputLine "> "
case minput of
Nothing -> outputStrLn "Goodbye."
Just input -> (liftIO $ process input) >> repl
main :: IO ()
main = runInputT defaultSettings repl