Initial commit

RPN.hs

@@ -0,0 +1,42 @@
+{-# LANGUAGE ViewPatterns #-}
+
+import Data.List
+
+main :: IO ()
+main = io (show . rpn)
+
+io :: (String -> String) -> IO ()
+io f = interact (unlines . map f . lines)
+
+rpn :: String -> Double
+rpn = head . foldl parse [] . words where
+  parse (y:x:xs) (flip lookup dyad  -> Just f) = f x y : xs
+  parse (x:xs)   (flip lookup monad -> Just f) = f x : xs
+  parse xs       (flip lookup nilad -> Just k) = k : xs
+  parse xs x = read x : xs
+
+-- dyadic functions
+dyad = [ ("+", (+))
+       , ("-", (-))
+       , ("*", (*))
+       , ("/", (/))
+       , ("^", (**)) ]
+
+-- monadic functions
+monad = [ ("sin"  , sin )
+        , ("asin" , asin)
+        , ("cos"  , cos )
+        , ("acos" , acos)
+        , ("tan"  , tan )
+        , ("atan" , atan)
+        , ("ln"   , log )
+        , ("sqrt" , sqrt)
+        , ("sgn"  , signum)
+        , ("abs"  , abs) 
+        , ("floor", fromIntegral . floor)
+        , ("ceil" , fromIntegral . ceiling) ]
+
+-- niladic functions
+nilad = [ ("pi" , pi)
+        , ("e"  , exp 1)
+        , ("phi", (1 + sqrt 5)/2) ]