Add line editing

hsilop.hs

@@ -1,25 +1,30 @@
 {-# LANGUAGE ViewPatterns #-}
 
 import Data.List
+import Data.Maybe
 import Text.Read
 import Text.Printf
 import Control.Monad
+import System.Console.Readline
 
 main :: IO ()
-main = io (result . rpn)
-
-
--- Interact line-by-line
-io :: (String -> String) -> IO ()
-io f = interact (unlines . map f . filter (not . null) . lines)
+main = do
+	line <- readline "ꟼ "
+	case fromMaybe "" line of
+		""  -> main
+		"q" -> return ()
+		exp -> do
+			putStrLn $ result (rpn exp) ++ "\n"
+			addHistory exp
+			main
 
 
 -- Pretty print RPN result/errors
 result :: Either String Double -> String
 result (Left err) = "Ꞥ∘ " ++ err
-result (Right x)  = printf ("ꟼ∘ " ++ format) x where
-  format | ceiling x == floor x = "%.0f"
-         | otherwise            = "%.10f"
+result (Right x)  = printf format x where
+  format | ceiling x == floor x = "∘ %.0f"
+         | otherwise            = "∘ %.10f"
 
 
 -- Solve a RPN expression