hw1: init

hw1/Calculator.hs

@@ -0,0 +1,36 @@
+-- This is a simple parser for testing out BigNum.
+-- Note that there are much better parsers, which
+-- we will explore in another class.
+
+import BigNum
+
+-- Crude way of handling whitespace: make sure
+-- that all ops are surrounded by whitespace.
+addSpace :: String -> String
+addSpace []       = ""
+addSpace ('+':xs) = " + " ++ addSpace xs
+addSpace ('-':xs) = " - " ++ addSpace xs
+addSpace ('*':xs) = " * " ++ addSpace xs
+addSpace ('^':xs) = " ^ " ++ addSpace xs
+addSpace (x:xs)   = x : addSpace xs
+
+calculate :: String -> BigNum -> BigNum -> BigNum
+calculate "+" b1 b2 = bigAdd b1 b2
+calculate "-" b1 b2 = bigSubtract b1 b2
+calculate "*" b1 b2 = bigMultiply b1 b2
+calculate "^" b1 b2 = bigPowerOf b1 b2
+
+main :: IO ()
+main = do
+  line <- getLine
+  if null line
+    then return ()
+    else do
+      case words $ addSpace line of
+          exp1:op:exp2:[] -> putStrLn $ prettyPrint $ calculate op big1 big2
+              where big1 = stringToBigNum exp1
+                    big2 = stringToBigNum exp2
+          exp:[] -> putStrLn $ show $ stringToBigNum exp
+          _ -> putStrLn "Only simply binary expressions are supported"
+      main
+