1 files changed, 50 insertions, 0 deletions
diff --git a/bin/Prompt.hs b/bin/Prompt.hs
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+++ b/bin/Prompt.hs
@@ -0,0 +1,50 @@
+-- |
+-- Copyright   : (c) 2015 Egor Tensin <Egor.Tensin@gmail.com>
+-- License     : MIT
+-- Maintainer  : Egor.Tensin@gmail.com
+-- Stability   : experimental
+-- Portability : portable
+
+module Prompt
+    ( withPrompt
+    , withoutPrompt
+    ) where
+
+import Control.Monad (void, when)
+import Control.Monad.Trans.Class  (lift)
+import Control.Monad.Trans.Except (ExceptT)
+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 <- 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 -> ExceptT IOError IO a -> ExceptT IOError IO Bool
+withPrompt msg m = do
+    lift $ do
+        putStr msg
+        hFlush stdout
+    agreed <- lift promptToContinue
+    when agreed $ void m
+    return agreed
+
+withoutPrompt :: ExceptT IOError IO a -> ExceptT IOError IO Bool
+withoutPrompt m = m >> return True