added parser and eval stub

Makefile

@@ -0,0 +1,2 @@
+all:
+	cabal install

bc.cabal

@@ -14,6 +14,6 @@ cabal-version:       >=1.10
 executable bc
   main-is:             Main.hs
   hs-source-dirs:      src/
-  build-depends:       base >=4.9 && <4.10, unix
+  build-depends:       base >=4.9 && <4.10, parsec, unix
   hs-source-dirs:      src
   default-language:    Haskell2010

src/BC/Eval.hs

@@ -0,0 +1,9 @@
+module BC.Eval (eval) where
+
+import BC.Types
+
+eval :: [Value] -> Value
+eval [x@(BInt _)] = x
+eval [(BOp  x)] = BErr ("operation " ++ x ++ " requires arguments")
+eval (x:xy) = x
+eval [] = BOp ""

src/BC/Parse.hs

@@ -0,0 +1,29 @@
+module BC.Parse (parse) where
+
+import qualified Text.ParserCombinators.Parsec as P
+
+import BC.Types
+
+symbol :: P.Parser Char
+symbol = P.oneOf "!%&|*+-/<=>^~"
+
+number :: P.Parser Value
+number = do
+    neg <- P.optionMaybe (P.string "-" P.<|> P.string "+")
+    x <- P.many1 P.digit
+    case neg of
+      Just "-" -> (return . BInt . read) ("-" ++ x)
+      _        -> (return . BInt . read) x
+
+operator :: P.Parser Value
+operator = do
+    res <- P.many1 $ P.letter P.<|> symbol
+    return $ BOp res
+
+parser :: P.Parser [Value]
+parser = (P.sepBy (P.try operator P.<|> number) P.spaces) <* P.eof
+
+parse :: String -> [Value]
+parse input = case P.parse parser input input of
+    Left err  -> [BErr $ show err]
+    Right val -> val

src/BC/Prompt.hs

@@ -5,6 +5,9 @@ import System.IO
 import System.Posix.Signals
 
 import BC.Config
+import BC.Eval
+import BC.Parse
+import BC.Types
 
 printHeader :: IO ()
 printHeader = do
@@ -14,33 +17,45 @@ printHeader = do
 
 
 output :: String -> IO ()
-output out = putStrLn $ returnStr ++ out
+output out =
+    let res = parse out
+    in if length res == 1 && isErr (res !! 0)
+      then putStrLn $ show (res !! 0)
+      else putStrLn $ returnStr ++ show (eval res)
 
 
 readline :: IO (Maybe String)
 readline = do
     putStr promptStr
-    hFlush stdout
     read' ""
   where read' acc = do
           c <- getChar
           case c of
             '\EOT' -> return Nothing
             '\n' -> return (Just acc)
-            c    -> read' (acc ++ [c])
+            '\DEL' ->
+              if length acc > 0
+              then do
+                putStr "\b \b"
+                read' (init acc)
+              else do
+                read' acc
+            c    ->
+              if isPrint c
+                then do
+                  putStr [c]
+                  read' (acc ++ [c])
+                else read' acc
 
 
 prompt :: IO ()
 prompt = do
     input <- readline
     case input of
-      Nothing -> do
+      Nothing -> putStrLn "Bye!"
-        output "Bye!"
+      Just "quit" -> putStrLn "Bye!"
-        return ()
-      Just "quit" -> do
-        output "Bye!"
-        return ()
       Just str -> do
+        putStrLn ""
         output str
         prompt
 
@@ -49,8 +64,8 @@ installHandlers :: IO ()
 installHandlers = do
     installHandler keyboardSignal (Catch (putStrLn "\n(interrupt) type quit to exit")) Nothing
     hSetBuffering stdout NoBuffering
+    hSetEcho stdin False
     hSetBuffering stdin NoBuffering
-    return ()
 
 
 startPrompt :: IO ()

src/BC/Types.hs

@@ -0,0 +1,13 @@
+module BC.Types where
+
+data Value = BInt Integer
+           | BOp String
+           | BErr String
+instance Show Value where
+  show (BInt i) = show i
+  show (BOp  o) = o
+  show (BErr e) = "error: " ++ e
+
+isErr :: Value -> Bool
+isErr (BErr _) = True
+isErr _        = False