EscapedSkolem错误在PureScript和Halogen中实现websocket重连接

Question

我正试图在PureScript中实现Websocket重连接，并且完全不知道如何继续。由于使用了Aff，我在顶层添加了重新连接代码；我认为这是正确的地方，但我不确定。

我试图在Haskell中实现它，但是由于EscapedSkolem中的runWs错误，我无法使它成为打字机。我给人的印象是，我可以通过添加一个类型签名来解决这个问题，但我无法在我的一生中知道签名可能是什么！

所以我有三个问题：

• 这是实现重连接的正确方式吗？
• runWs的类型是什么(关于我如何为自己解决这个问题的任何提示都会很棒)？
• 如果添加类型签名不能修复EscapedSkolem错误，我将如何修复它？

最后，当涉及到PureScript时，我是一个完整的新手，所以如果有什么不清楚的地方，请指出这一点，我会尽力澄清。

编辑：添加了错误编译器输出并稍微更改了标题。

module Main where

import Prelude

import Control.Coroutine (Producer, Consumer, runProcess, consumer, ($$))
import Control.Coroutine.Aff (produce)

import Control.Monad.Aff (Aff, delay)
import Control.Monad.Aff.AVar (AVAR)
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)
import Control.Monad.Eff.Exception (EXCEPTION)
import Control.Monad.Eff.Ref (REF)
import Control.Monad.Eff.Var (($=), get)

import DOM (DOM)
import DOM.Websocket.Event.CloseEvent (reason)


import Data.Either (Either(..))
import Data.Maybe (Maybe(..))
import Data.Time.Duration (Milliseconds(..))
import Halogen as H
import Halogen.Aff (HalogenEffects, awaitBody, runHalogenAff)
import Halogen.VDom.Driver (runUI)
import Log (Query(..), component)
import WebSocket (Connection(..), URL(..), WEBSOCKET, newWebSocket, runMessage, runURL, runMessageEvent)


wsURI :: URL
wsURI = URL "ws://localhost:6385"


reconnectionDelay :: Milliseconds
reconnectionDelay = Milliseconds 10000.0


main :: forall eff. Eff (HalogenEffects (console :: CONSOLE, err :: EXCEPTION , avar :: AVAR , dom :: DOM , exception :: EXCEPTION , ref :: REF , ws :: WEBSOCKET | eff)) Unit
main = do
  runHalogenAff do
    body <- awaitBody
    driver <- runUI component unit body

    ---> Replace this: <---
    runProcess (wsProducer $$ wsConsumer driver.query)
    ---> with this: <---
    --   runWs driver

-- -------------------------------------------------
-- -------------------------------------------------
--
-- Reconnection function
-- runWs :: ????????
runWs p = go
  where
    go = do
      runProcess (wsProducer $$ wsConsumer p)
      delay reconnectionDelay
      go

-- -------------------------------------------------
-- -------------------------------------------------


wsProducer :: forall eff. Producer String (Aff (console :: CONSOLE, err :: EXCEPTION , ws :: WEBSOCKET , avar :: AVAR | eff)) Unit
wsProducer = produce \emit -> do

  Connection socket <- newWebSocket wsURI []

  socket.onopen $= \event -> do
    log "onopen: Connection opened"
    log <<< runURL =<< get socket.url


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


  socket.onclose $= \event -> do
    log $ "Socket Closed, returning to runHalogenAff: "  <> reason event
    emit $ Right unit


  socket.onerror $= \event -> do
    log "Error."
    emit $ Right unit


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

编译器的输出是：

Compiling Main
[1/1 MissingTypeDeclaration] src/Main.purs:54:1

      v
  54  runWs p = go
  55    where
  56      go = do
  57        runProcess (wsProducer $$ wsConsumer p)
  58        delay reconnectionDelay
  59        go
            ^

  No type declaration was provided for the top-level declaration of runWs.
  It is good practice to provide type declarations as a form of documentation.
  The inferred type of runWs was:

    forall t110 t120.
      (Query a0
      -> Aff
            ( avar :: AVAR
            , ref :: REF
            , exception :: EXCEPTION
            , dom :: DOM
            , console :: CONSOLE
            , err :: EXCEPTION
            , ws :: WEBSOCKET
            | t120
            )
            a0
      )
      -> Aff
          ( console :: CONSOLE
          , err :: EXCEPTION
          , ws :: WEBSOCKET
          , avar :: AVAR
          , dom :: DOM
          , exception :: EXCEPTION
          , ref :: REF
          | t120
          )
          t110

  where a0 is a rigid type variable
          bound at line 57, column 44 - line 57, column 45

[1/1 EscapedSkolem] src/Main.purs:54:1

      v
  54  runWs p = go
  55    where
  56      go = do
  57        runProcess (wsProducer $$ wsConsumer p)
  58        delay reconnectionDelay
  59        go
            ^

  The type variable a, bound at

    /home/rgh/dev/purescript/translate/sidebar/src/Main.purs line 57, column 44 - line 57, column 45

  has escaped its scope, appearing in the type

    (Query a2
    -> Aff
          ( avar :: AVAR
          , ref :: REF
          , exception :: EXCEPTION
          , dom :: DOM
          , console :: CONSOLE
          , err :: EXCEPTION
          , ws :: WEBSOCKET
          | t120
          )
          a2
    )
    -> Aff
        ( console :: CONSOLE
        , err :: EXCEPTION
        , ws :: WEBSOCKET
        , avar :: AVAR
        , dom :: DOM
        , exception :: EXCEPTION
        , ref :: REF
        | t120
        )
        t110

  in the expression \p ->
                      let
                        go = ...
                      in go
  in value declaration runWs

          Src   Lib   All
Warnings   1     0     1
Errors     1     0     1
* Failed to rebuild; try to fix the compile errors

Answer 1

编译器错误消息有时可能很难解密，但在这种情况下，它是您正在寻找的答案。让我们看看这里的do区：

do
  runHalogenAff do
    body <- awaitBody
    driver <- runUI component unit body
    runWs driver.query -- < assuming you made a small mistake here

我通常从desugaring开始，我发现它使跟踪类型变得更容易，但是ymmv：

runHalogenAff $
  awaitBody >>= \body ->
    runUI component unit body >>= \driver ->
      runWs driver.query

查看runHalogenAff的签名，我们可以看到它接受Aff (HalogenEffects eff) x类型的参数，这意味着下面的术语必须计算为该类型的值。然后，runWs必须返回该类型的值。

现在让我们转到runWs。它的论点是f ~> m，在您的示例中，它是蒙纳德。我们可以将其写下来，并要求编译器为我们找出其余的内容：

runWs :: (Query ~> Aff _) -> Aff _ Unit

这将成功地建设，并给你什么，你可以填补这些漏洞。这是最后的签名：

runWs :: forall eff. 
      (Query ~> Aff (HalogenEffects 
        ( console :: CONSOLE
        , err :: EXCEPTION
        , ws :: WEBSOCKET
        | eff
        )))
      -> Aff (HalogenEffects
        ( console :: CONSOLE
        , err :: EXCEPTION
        , ws :: WEBSOCKET
        | eff
        )) Unit

实际上，这正是编译器输出提供给您的。我假设错误消息“类型变量a已转义其作用域”是因为自然变换的定义中的通用量词。