Automatic decoding of supported literals in REPL

Automatic decoding & display of string, number, and list types in REPL.
General updates to README, style, and comments.

src/REPL.hs

@@ -11,19 +11,29 @@ import System.IO            (hFlush, stdout)
 
 repl :: Map.Map String T -> IO ()
 repl env = do
-  putStr "sapling > "
+  putStr "sapling < "
   hFlush stdout
   input <- getLine
   if input == "_:exit"
     then putStrLn "Goodbye!"
   else if input == ""
-    then do 
+    then do
       putStrLn ""
       repl env
     else do
       let clearEnv = Map.delete "__result" env
       let newEnv   = evalSingle clearEnv (parseSingle input)
       case Map.lookup "__result" newEnv of
-        Just r  -> putStrLn $ "sapling < " ++ show r
+        Just r  -> do
+          putStrLn $ "sapling > " ++ show r
+          putStrLn $ "DECODE -: " ++ (decodeResult r)
         Nothing -> pure ()
       repl newEnv
+
+decodeResult :: T -> String
+decodeResult tc = 
+  case ofString tc of
+    Right str -> "\"" ++ str ++ "\""
+    Left _ -> case ofNumber tc of
+      Right num -> "Number: " ++ show num
+      Left _ -> "Failed to decode number from Tree"