tasks a-s

Task/Non-continuous-subsequences/Haskell/non-continuous-subsequences-1.hs

@@ -0,0 +1,9 @@
+action p x = if p x then succ x else x
+
+fenceM p q s []     = guard (q s) >> return []
+fenceM p q s (x:xs) = do
+  (f,g) <- p
+  ys <- fenceM p q (g s) xs
+  return $ f x ys
+
+ncsubseq = fenceM [((:), action even), (flip const, action odd)] (>= 3) 0