haskelline_state.hs

-- Notes on how to wrap InputT over StateT to maintain the environment around a language repl.

type HaskellLineT = InputT (StateT Env IO) ()

runScriptInteractive = runStateT (runInputT defaultSettings loop) (initEnv Nothing)
  where
    loop :: HaskellLineT
    loop = do
      minput <- getInputLine "%"
      when (isNothing minput) loop
      env <- lift get
      let lex_result = scanner (fromJust minput)
      case lex_result of
        Right lex -> do
          let ast = P.parse loxProgram "" lex
          case ast of
            Right ast' -> do
              (env', msg) <- liftIO $ interpretProgram ast' env
              when (isJust msg) $ liftIO $ print msg
              lift $ put env'
              loop
            Left e -> do
              liftIO $ print $ "Scanner error" <> show e
              loop
        Left e -> do
          liftIO $ print $ "Lexer error" <> show e
          loop