path: root/apps/Prompt.hs

{-
 - Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
 - This file is licensed under the terms of the MIT License.
 - See LICENSE.txt for details.
-}

module Prompt
    ( withPrompt
    , withoutPrompt
    , promptUnless
    ) where

import Control.Monad (liftM, void, when)
import Data.Char     (toLower)
import System.IO     (hFlush, stdout)

prompt :: String -> IO String
prompt msg = do
    putStr msg
    hFlush stdout
    getLine

promptYesNo :: String -> IO Bool
promptYesNo msg = do
    response <- liftM (map toLower) $ prompt msg
    if response `elem` yeses
        then return True
        else if response `elem` noes
            then return False
            else promptToContinue
  where
    yeses = ["y", "yes"]
    noes = ["n", "no"]
    
promptToContinue :: IO Bool
promptToContinue = promptYesNo "Continue? (y/n) "

withPrompt :: String -> IO a -> IO Bool
withPrompt msg m = do
    putStr msg
    hFlush stdout
    agreed <- promptToContinue
    when agreed $ void m
    return agreed

withoutPrompt :: IO a -> IO Bool
withoutPrompt m = m >> return True

promptUnless :: Bool -> String -> IO a -> IO Bool
promptUnless skipPrompt msg
    | skipPrompt = withoutPrompt
    | otherwise  = withPrompt msg