I'm trying to implement Websocket reconnection in PureScript and am at a complete loss at how to proceed. I've added the reconnection code at the top level due to the use of Aff; I think this is the correct place but I'm not sure.
I've tried to implement it as I might in Haskell but I can't make it typecheck due to an EscapedSkolem error in runWs. I get the impression I can fix this by adding a type signature but I can't for the life of me work out what the signature might be!
So I have three questions:
- Is this the correct way of implementing reconnection?
- What is the type of
runWs(any hints on how I might work this out for myself would be fantastic)? - If adding a type signature doesn't fix the
EscapedSkolemerror how would I go about fixing it?
And finally, I'm a complete newb when it comes to PureScript so if anything's unclear please point that out and I'll try and clarify.
EDIT: Added the error compiler output and changed the title slightly.
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 $$ wsConsumer p)
delay reconnectionDelay
go
-- -------------------------------------------------
-- -------------------------------------------------
wsProducer :: forall eff. Producer String (Aff (console :: CONSOLE, err :: EXCEPTION , ws :: WEBSOCKET , avar :: AVAR | eff)) Unit
wsProducer = produce \emit -> do
Connection socket <- newWebSocket wsURI []
socket.onopen $= \event -> do
log "onopen: Connection opened"
log <<< runURL =<< get socket.url
socket.onmessage $= \event -> do
emit $ Left $ runMessage (runMessageEvent event)
socket.onclose $= \event -> do
log $ "Socket Closed, returning to runHalogenAff: " <> reason event
emit $ Right unit
socket.onerror $= \event -> do
log "Error."
emit $ Right unit
wsConsumer :: forall eff . (Query ~> Aff (HalogenEffects eff)) -> Consumer String (Aff (HalogenEffects eff)) Unit
wsConsumer driver = consumer \msg -> do
driver $ H.action $ AddMessage msg
pure Nothing
And the compiler output is:
Compiling Main
[1/1 MissingTypeDeclaration] src/Main.purs:54:1
v
54 runWs p = go
55 where
56 go = do
57 runProcess (wsProducer $$ 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
