PureScript卤素和websockets

Question

我正在尝试将purescript-halogen与websockets结合使用，但经过多次尝试，我无法使它们一起工作。

我已经看到了this question on Thermite and websockets和菲尔关于Driver函数的答案。卤素也有一个Driver函数，但是我需要用Aff效应运行Driver函数，而purescript-websockets-simple使用Eff效应。

我不知道如何将websocket包的同步回调转换为运行在Aff monad中的异步代码。我需要使用AVar吗？我需要purescript-coroutines-aff吗？如果是的话，我该如何将这些部件连接在一起呢？

预先感谢任何正确方向的指点！

Answer 1

在这种情况下，您确实希望使用purescript-aff-coroutines。这将为您提供一个协同线Producer，然后您可以连接到一个将消息推入驱动程序的Consumer：

module Main where

import Prelude

import Control.Coroutine (Producer, Consumer, consumer, runProcess, ($$))
import Control.Coroutine.Aff (produce)
import Control.Monad.Aff (Aff)
import Control.Monad.Aff.AVar (AVAR)
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Exception (EXCEPTION)
import Control.Monad.Eff.Var (($=))

import Data.Array as Array
import Data.Either (Either(..))
import Data.Maybe (Maybe(..))

import Halogen as H
import Halogen.HTML.Indexed as HH
import Halogen.Util (runHalogenAff, awaitBody)

import WebSocket (WEBSOCKET, Connection(..), Message(..), URL(..), runMessageEvent, runMessage, newWebSocket)

----------------------------------------------------------------------------
-- Halogen component. This just displays a list of messages and has a query
-- to accept new messages.
----------------------------------------------------------------------------

type State = { messages :: Array String }

initialState :: State
initialState = { messages: [] }

data Query a = AddMessage String a

ui :: forall g. H.Component State Query g
ui = H.component { render, eval }
  where
  render :: State -> H.ComponentHTML Query
  render state =
    HH.ol_ $ map (\msg -> HH.li_ [ HH.text msg ]) state.messages

  eval :: Query ~> H.ComponentDSL State Query g
  eval (AddMessage msg next) = do
    H.modify \st -> { messages: st.messages `Array.snoc` msg }
    pure next

----------------------------------------------------------------------------
-- Websocket coroutine producer. This uses `purescript-aff-coroutines` to
-- create a producer of messages from a websocket.
----------------------------------------------------------------------------

wsProducer :: forall eff. Producer String (Aff (avar :: AVAR, err :: EXCEPTION, ws :: WEBSOCKET | eff)) Unit
wsProducer = produce \emit -> do
  Connection socket <- newWebSocket (URL "ws://echo.websocket.org") []

  -- This part is probably unnecessary in the real world, but it gives us 
  -- some messages to consume when using the echo service
  socket.onopen $= \event -> do
    socket.send (Message "hello")
    socket.send (Message "something")
    socket.send (Message "goodbye")

  socket.onmessage $= \event -> do
    emit $ Left $ runMessage (runMessageEvent event)

----------------------------------------------------------------------------
-- Coroutine consumer. This accepts a Halogen driver function and sends
-- `AddMessage` queries in when the coroutine consumes an input.
----------------------------------------------------------------------------

wsConsumer
  :: forall eff
   . (Query ~> Aff (H.HalogenEffects (ws :: WEBSOCKET | eff)))
  -> Consumer String (Aff (H.HalogenEffects (ws :: WEBSOCKET | eff))) Unit
wsConsumer driver = consumer \msg -> do
  driver $ H.action $ AddMessage msg
  pure Nothing

----------------------------------------------------------------------------
-- Normal Halogen-style `main`, the only addition is a use of `runProcess`
-- to connect the producer and consumer and start sending messages to the
-- Halogen component.
----------------------------------------------------------------------------

main :: forall eff. Eff (H.HalogenEffects (ws :: WEBSOCKET | eff)) Unit
main = runHalogenAff do
  body <- awaitBody
  driver <- H.runUI ui initialState body
  runProcess (wsProducer $$ wsConsumer driver)
  pure unit

这将为您提供一页几乎立即打印的页面：

1. 你好
2. 某物
3. 再见

但它能做你想做的一切，诚实！如果你使用生产者的“真实”来源，你会得到更多的东西，你需要什么。