arrows

We know free monads are useful, and packages like Operational make it easy to define new monads by only caring about the application-specific effects, not the monadic structure itself. We can easily define "free arrows" analogous to how free monads are defined: {-# LANGUAGE GADTs #-} module FreeA ( FreeA, effect ) where import Prelude hiding ((.), id) import Control.Category import Control.Arrow import Control.Applicative import Data.Monoid data FreeA eff a b where Pure :: (a -> b) -> FreeA eff a b Effect :: eff a b -> FreeA eff a b Seq :: FreeA eff a b -> FreeA eff b c -> FreeA eff a c Par ::

I've been trying to get a grip on arrows since they're the basis of most FRP implementations. I think I understand the basic idea - they're related to monads but store static information at each bind operator so you can walk through a chain of arrows and look at the static information without having to evaluate the whole arrow. But I get lost at the point where we start discussing first, second, and swap. What do 2-tuples have to do with arrows? Tutorials present the tuple stuff as if it were an obvious next step, but I'm not really seeing the connection. For that matter, what does the arrow

I'm broadly familiar with the concepts of monads and arrows as used in functional programming. I also understand that they can be used to solve similar kinds of problems. However, I'm still a bit confused about how to select which one to use in any given situation. When should I use monads and when should I use arrows? sclv There are two excellent papers by Lindley, Wadler & Yallop (discussed at LTU here ). The most important thing to understand is that there are more things which are arrows than there are things which are monads. Conversely, monads are strictly more powerful than arrows (the

I am trying to create a game using Haskell + Netwire 5 (+ SDL). Now I am working on the output part, where I would like to create wires that read in some game state and output the SDL surfaces to be blitted on screen. However, the problem is that SDL surfaces are contained in IO monad, so any function that creates such surfaces must have type a -> IO b . Of course, arr does not construct a Wire from a -> m b . However, since the type signature of a wire is (Monad m, Monoid e) => Wire s e m a b , it looks quite like a Kleisi Arrow, but I cannot find a suitable constructor for making such a wire

I'm creating a graph in JavaFX which is supposed to be connected by directed edges. Best would be a bicubic curve. Does anyone know how to do add the arrow heads? The arrow heads should of course be rotated depending on the end of the curve. Here's a simple example without the arrows: import javafx.application.Application; import javafx.scene.Group; import javafx.scene.Scene; import javafx.scene.paint.Color; import javafx.scene.shape.CubicCurve; import javafx.scene.shape.Rectangle; import javafx.stage.Stage; public class BasicConnection extends Application { public static void main(String[]