frp | 易学教程

RxJs: how to get values emitted before we subscribe?

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问题 With RxJs, once we start subscribe to an observable, we will start getting values once they are emitted, but how do I get all the values emitted by an observable before I've subscribed to it? 回答1: An observable is just a function that returns 0 or more values between now and the end of time. Like any other function it doesn't do anything before it's called (subscribed to). That being said, you can transform your observable to a hot observable by calling: // This makes the observable

Reactive Cocoa limit a signal to only one subscriber at once

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问题 I need to model following in RAC. I have a tabBarController which will subscribe to a notification signal. Say push notification. Also say currently active view controller may also be want to subscribe to the same signal. But if any view controller subscribed to it tabBarController doesn't want to handle it. Otherwise it will handle it. Also when current visible view controller changes. It needs to delegate back the responsibility to tabController. Currently without RAC I maintain array of

Is it possible?: Behavior t [Behavior t a] -> Behavior t [a]

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问题 Is there a way to have a Behavior t [a] where the values of [a] at time t are the values contained in a Behavior t [Behavior t a] at time t? I.e, a function with the type of: Behavior t [Behavior t a] -> Behavior t [a] If this is not possible, is that because of a logical impossibility or a limitation in reactive-banana? 回答1: The type is trivially inhabited for any Applicative : {-# LANGUAGE RankNTypes #-} import Control.Applicative import Control.Monad import Data.Functor.Identity import

Why is there no mapM for repa arrays?

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问题 Background I am using repa more as a "management" tool. I pass around reactive-banana s AddHandlers in an Array : Array D DIM2 (AddHandler Bool) . Currently I am using this kludge: mapMArray :: (Monad m, R.Source r a, R.Shape sh) => (a -> m b) -> Array r sh a -> m (Array D sh b) mapMArray f a = do l <- mapM f . R.toList $ a return $ R.fromFunction sh (\i -> l !! R.toIndex sh i) where sh = R.extent a So I can do something like this: makeNetworkDesc :: Frameworks t => Array D DIM2 (AddHandler

What is the inverse of a promise?

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问题 A promise represents a value that might become available in the future (or fails to do so). What I am looking for is a data type which represents an available value that might become unavailable in the future (possibly due to an error): Promise a b = TransitionFromTo<PENDING, Either<value a, error b>> ??? a = TransitionFromTo<value a, Either<ENDED, FAILED>> or ??? a b = TransitionFromTo<value a, Either<ENDED, error b>> Has such a concept (or similar) been explored already? Are there existing

tmux常用命令

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有些功能是需要通过后台进程一直运行或启动着的，就像frp穿透功能在启用穿透之前，需要先启动会话，且保持终端连接关闭后，该穿透会话处于运行状态。 //启动新会话 1.tmux new -s frp //进行frp目录，进行启用穿透功能 2. cd ~/software/frp文件夹 ./frpc -c frpc.ini //关闭会话detached,进入终端，此时穿透会话仍然运行中 3.ctrt+b d ———————————————————————————————————————————— 4.在终端查看开启的会话 tmux ls 5.从终端进入某个会话 tmux a -t frp 6.销毁某个会话 tmux kill-session -t frp 来源： CSDN 作者：雁听雨链接： https://blog.csdn.net/weixin_37194611/article/details/103454349

Simple Example for Scala React

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问题 Based on the paper Deprecating the Observer Pattern with Scala.React I tried to set up a simple example from the paper, but it throwed an exception Exception in thread "main" java.lang.AssertionError: assertion failed: This method must be run on its domain scala.react.NilDebug@1502c065 A related question is Running a simple Scala.React expression. How do I set up everything to use the great power of the scala react library? Besides the library scala-react, I used the following example: object

F# observable filter with side effect

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问题 I have a number of events that are merged into one observable that executes some commands. If a command succeeded some result takes place. In addition, the command should be logged. In terms of code, this looks like let mevts = modifyingevents |> Observable.filter exec_action |> Observable.add (fun action -> self.OutlineEdited <- true) where the function exec_action results in some side effect such as editing a treeview. If this succeeded then the property OutlineEdited is set to true . I was

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