reactive-banana | 易学教程

How does Reactive Banana's mapAccum function work?

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问题 I have looked at a number answers to questions here on Stack Overflow trying to find a solution to my problem in using the Reactive Banana library. All the answers use some magic using 'mapAccum' that I can't quite understand. Looking at the API documentation all I find is "Efficient combination of accumE and accumB ." which is not very helpful. It seems that this function can be used to compare the values of a Behavior at the time of two consecutive events which is what I'd like to do. But I

Execute MonadIO action inside of reactimate

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问题 In reactive-banana, I am trying to run reactimate :: Event (IO ()) -> Moment () with some actions of Arduino in hArduino package, an instance of MonadIO . There seems no function of Arduino a -> IO a provided in the package. How would you execute Arduino actions in reactimate ? 回答1: How would you execute Arduino actions in reactimate ? I would cause them to be executed indirectly, by executing an IO action which has an observable side-effect. Then, inside withArduino , I would observe this

Implementing a timer in Traveller game

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This problem is a continuation of what I started here . I'm using the asteroid example as a model to work from. The problem I want to talk about here is the one of a timer. The asteroids example uses the event0 function to make one, which relies on the Graphics.UI.WX library. I don't want to use WX for this project. Could someone tell me what event0 is doing generally, so that I can figure out what I need to do to make a similar function? To bind reactive-banana to an external event-based framework, be it WX or any other, have a look at the Reactive.Banana.Frameworks module. The event0

How to implement reactive-banana behaviors that recursively depend on themself?

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问题 I have a Behavior whose value I want to change based on the occurrence of an Event and the Behavior's current value. In the example below I have two counters that are updated based on whether a boolean behaviour is True or False. As it is this code crashes with a <<loop>> exception, but I'm unsure how to restructure it to work or how else to approach this problem. {-# LANGUAGE ScopedTypeVariables #-} import Reactive.Banana import Reactive.Banana.Frameworks import Control.Arrow import Control

Execute MonadIO action inside of reactimate

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In reactive-banana, I am trying to run reactimate :: Event (IO ()) -> Moment () with some actions of Arduino in hArduino package , an instance of MonadIO . There seems no function of Arduino a -> IO a provided in the package. How would you execute Arduino actions in reactimate ? How would you execute Arduino actions in reactimate ? I would cause them to be executed indirectly, by executing an IO action which has an observable side-effect. Then, inside withArduino , I would observe this side-effect and run the corresponding Arduino command. Here's some example code. First, let's get the imports

Testing in reactive-banana

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问题 Is there a way to unit test networks created in reactive banana? Say I've built up some network with some input events - is it possible to verify that events have produced some output stream/behaviours have some value after some number of input events. Does it even make sense to do this? I noticed there are various interpret* functions but couldn't seem to work out how to use them. There's also the Model module which looks ideal for testing but has completely different types to the real

reactive-banana: Firing event that contain the most up to date value of a Behavior

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问题 Suppose I have an event trigger which I want to do two things when fired. First, I want it to update the value of some behavior . Second, if other conditions are met, I want it to fire another event send_off with the updated value of the behavior. Expressed in code form, suppose I have trigger :: Event b trigger = ... updateFromTrigger :: b -> (a -> a) updateFromTrigger = ... conditionFromTrigger :: b -> Bool conditionFromTrigger = ... behavior :: Behavior a behavior = accumB initial_value

How to implement reactive-banana behaviors that recursively depend on themself?

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I have a Behavior whose value I want to change based on the occurrence of an Event and the Behavior's current value. In the example below I have two counters that are updated based on whether a boolean behaviour is True or False. As it is this code crashes with a <<loop>> exception, but I'm unsure how to restructure it to work or how else to approach this problem. {-# LANGUAGE ScopedTypeVariables #-} import Reactive.Banana import Reactive.Banana.Frameworks import Control.Arrow import Control.Concurrent import Control.Monad import Control.Monad.Fix counter :: Bool -> Event t Int -> Behavior t

reactive-banana: How to create an AddHandler?

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I'm currently trying to get to know FRP through Heinrich Apfelmus' reactive-banana , which seems to be a quite well documented and simple library, compared to the other ones I've looked at. However, I can't wrap my head around the AddHandler type. Let's say I want to use GLFW to get mouse button clicks so that I have something like eMouseButton :: Event () . Looking at the examples, it seems that I'd somehow have to use fromAddHandler , but I have no idea how to assemble that AddHandler argument. I think I'll have to use newAddHandler somehow, but how? I guess an example of how to connect

Testing in reactive-banana

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Is there a way to unit test networks created in reactive banana? Say I've built up some network with some input events - is it possible to verify that events have produced some output stream/behaviours have some value after some number of input events. Does it even make sense to do this? I noticed there are various interpret* functions but couldn't seem to work out how to use them. There's also the Model module which looks ideal for testing but has completely different types to the real implementation. When you say "unit test," I'm imagining something like QuickCheck , where you inject a