Data commit

Task/Population-count/Idris/population-count.idris

@@ -0,0 +1,40 @@
+module Main
+import Data.Vect
+
+isOdd : (x : Int) -> Bool
+isOdd x = case mod x 2 of
+            0 => False
+            1 => True
+
+popcnt : Int -> Int
+popcnt 0 = 0
+popcnt x = case isOdd x of
+  False => popcnt (shiftR x 1)
+  True => 1 + popcnt (shiftR x 1)
+
+isOdious : Int -> Bool
+isOdious k = isOdd (popcnt k)
+
+isEvil : Int -> Bool
+isEvil k = not (isOdious k)
+
+filterUnfoldN : (n : Nat) ->
+                (pred : Int -> Bool) -> (f : Int -> a) ->
+                (next : Int -> Int) -> (seed : Int) ->
+                Vect n a
+filterUnfoldN Z pred f next seed = []
+filterUnfoldN (S k) pred f next seed =
+  if pred seed
+  then (f seed) :: filterUnfoldN k pred f next (next seed)
+  else filterUnfoldN (S k) pred f next (next seed)
+
+printCompact : (Show a) => Vect n a -> IO ()
+printCompact v = putStrLn (unwords (map show (toList v)))
+
+main : IO ()
+main = do putStr "popcnt(3**i): "
+          printCompact (filterUnfoldN 30 (\_ => True) popcnt (3 *) 1)
+          putStr "Evil:         "
+          printCompact (filterUnfoldN 30 isEvil id (1 +) 0)
+          putStr "Odious:       "
+          printCompact (filterUnfoldN 30 isOdious id (1 +) 0)