Just another update

Task/Averages-Simple-moving-average/Haskell/averages-simple-moving-average-1.hs

@@ -0,0 +1,26 @@
+import Control.Monad
+import Data.List
+import Data.IORef
+
+mean :: Fractional a => [a] -> a
+mean xs = sum xs / (genericLength xs)
+
+series = [1,2,3,4,5,5,4,3,2,1]
+
+simple_moving_averager period = do
+  numsRef <- newIORef []
+  return (\x -> do
+            nums <- readIORef numsRef
+            let xs = take period (x:nums)
+            writeIORef numsRef xs
+            return $ mean xs
+         )
+
+main = do
+  sma3 <- simple_moving_averager 3
+  sma5 <- simple_moving_averager 5
+  forM_ series (\n -> do
+                mm3 <- sma3 n
+                mm5 <- sma5 n
+                putStrLn $ "Next number = " ++ (show n) ++ ", SMA_3 = " ++ (show mm3) ++ ", SMA_5 = " ++ (show mm5)
+               )

Task/Averages-Simple-moving-average/Haskell/averages-simple-moving-average-3.hs

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+import Control.Monad
+import Control.Monad.State
+
+period :: Int
+period = 3
+
+type SMAState = [Float]
+
+computeSMA :: Float -> State SMAState Float
+computeSMA x = do
+  previousValues <- get
+  let values = previousValues ++ [x]
+  let newAverage = if length values <= period then (sum values) / (fromIntegral $ length remainingValues :: Float)
+                   else (sum remainingValues) / (fromIntegral $ length remainingValues :: Float)
+                     where remainingValues = dropIf period values
+  put $ dropIf period values
+  return newAverage
+
+dropIf :: Int -> [a] -> [a]
+dropIf x xs = drop ((length xs) - x) xs
+
+demostrateSMA :: State SMAState [Float]
+demostrateSMA = mapM computeSMA [1, 2, 3, 4, 5, 5, 4, 3, 2, 1]
+
+main :: IO ()
+main = putStrLn $ (show result)
+        where
+         (result, _) = runState demostrateSMA []