Turn debugTerminalKeys into a single loop. (#111)

Make it a looped KeyCommand inside a single call to runInputCmdT,
rather than calling runInputCmdT once for each character.

This removes some noise by letting us clear the prompt before printing the key that was read. 
 It also hopefully makes it closer to "real" results when entering multiple keys (e.g., holding them down).

Author: judah

System/Console/Haskeline/Internal.hs

@@ -1,7 +1,6 @@
 module System.Console.Haskeline.Internal
     ( debugTerminalKeys ) where
 
-import Control.Monad (forever)
 import System.Console.Haskeline (defaultSettings, outputStrLn)
 import System.Console.Haskeline.Command
 import System.Console.Haskeline.InputT
@@ -19,16 +18,20 @@ import System.Console.Haskeline.Term
 -- Haskeline's behavior may be modified by editing your @~/.haskeline@
 -- file.  For details, see: <https://github.com/judah/haskeline/wiki/CustomKeyBindings>
 --
-debugTerminalKeys :: IO ()
+debugTerminalKeys :: IO a
 debugTerminalKeys = runInputT defaultSettings $ do
     outputStrLn
         "Press any keys to debug Haskeline's input, or ctrl-c to exit:"
     rterm <- InputT ask
     case termOps rterm of
         Right _ -> error "debugTerminalKeys: not run in terminal mode"
-        Left tops -> forever $ getKey tops >>= outputStrLn . show
+        Left tops -> runInputCmdT tops $ runCommandLoop tops prompt
+                                            loop emptyIM
   where
-    getKey tops = runInputCmdT tops
-                    $ runCommandLoop tops prompt getKeyCmd emptyIM
-    getKeyCmd = KeyMap $ \k -> Just $ Consumed $ const $ return k
+    loop = KeyMap $ \k -> Just $ Consumed $
+            (const $ do
+                effect (LineChange $ const ([],[]))
+                effect (PrintLines [show k])
+                setState emptyIM)
+            >|> keyCommand loop
     prompt = stringToGraphemes "> "