REPL.hs

--
-- Copyright (c) 2005 Lennart Augustsson
-- See LICENSE for licensing details.
--
module REPL(REPL(..), repl) where
import qualified Control.Exception
import System.Console.Readline(readline, addHistory)

data REPL s = REPL {
    repl_init :: IO (String, s),		-- prompt and initial state
    repl_eval :: s -> String -> IO (Bool, s),		-- quit flag and new state
    repl_exit :: s -> IO ()
    }

repl :: REPL s -> IO ()
repl p = do
    (prompt, state) <- repl_init p
    let loop s = (do
	    mline <- readline prompt
	    case mline of
		Nothing -> loop s
		Just line -> do
		    (quit, s') <- repl_eval p s line
		    if quit then
			repl_exit p s'
		     else do
			addHistory line
			loop s'
	    ) `Control.Exception.catch` ( \ exc ->
		do
		    putStrLn $ "\nInterrupted (" ++ show exc ++ ")"
		    loop s
	    )
    loop state