tasks a-s

Task/Parsing-RPN-calculator-algorithm/Haskell/parsing-rpn-calculator-algorithm.hs

@@ -0,0 +1,15 @@
+import Data.List (elemIndex)
+
+-- Show results
+main = mapM_ (\(x, y) -> putStrLn $ x ++ " ==> " ++ show y) $ reverse $ zip b (a:c)
+        where (a, b, c) = solve "3 4 2 * 1 5 - 2 3 ^ ^ / +"
+
+-- Solve and report RPN
+solve = foldl reduce ([], [], []) . words
+reduce (xs, ps, st) w =
+    if i == Nothing
+        then (read w:xs, ("Pushing " ++ w):ps, xs:st)
+        else (([(*),(+),(-),(/),(**)]!!o) a b:zs, ("Performing " ++ w):ps, xs:st)
+    where   i = elemIndex (head w) "*+-/^"
+            Just o = i
+            (b:a:zs) = xs