Hi all, I want to control the bulb using stream of signals. Each signal from the stream just toggle the bulb. I have no idea how to connect the pieces togheter. I have been trying to use for-comprehension but without any success. I have something like this at the moment.
val signal1 = Stream.repeatEval(producer("A", 100.millis))
val signal2 = Stream.repeatEval(producer("B", 200.millis))
val signal: Stream[IO, String] = signal1.merge(signal2)
class Bulb(ref: Ref[IO, Int]) {
def toggle(): IO[Unit] = IO.println(("toggle")) >> IO.unit //todo
}
def pipes(bulb: Bulb): Pipe[IO, String, String] = in =>
in.evalMap(signal => bulb.toggle() >> IO("Toggled"))
val ioBulb: IO[Bulb] = for {
r <- Ref[IO].of(0)
b = new Bulb(r)
} yield bayeo (ayeo) assuming every toggle sets the internal Ref to either 1 or 0, you can do something like this.
object Main extends IOApp.Simple:
val signal1 = Stream.emit[IO, String]("A").metered(100.millis)
val signal2 = Stream.emit[IO, String]("B").metered(200.millis)
def run: IO[Unit] =
Bulb.make[IO].flatMap { bulb =>
signal1
.merge(signal2)
.evalMap(_ => IO.println("toggle") *> bulb.toggle)
.interruptAfter(5.seconds)
.compile
.drain
}
trait Bulb[F[_]]:
def toggle: F[Unit]
object Bulb:
def make[F[_]: Functor: Ref.Make]: F[Bulb[F]] =
Ref[F].of(0).map { ref =>
new:
def toggle: F[Unit] = ref.update(x => if x == 0 then 1 else 0)
}Sleeps and timeouts don't work so well in the browser but you can see the compiling version here: https://scastie.scala-lang.org/NXdBGJLZTwyJeFh3tsgIwg
Hello everyone,
Sorry if noob question, but I don't understand why using an instance of Async[F] where F is an effect monad, basically gives us access to the methods in MonadError too.
Async doesn't seem to extends MonadError...
Does Async have MonadError instances available regardless of what F is?
Sorry if noob question, but I don't understand why using an instance of Async[F] where F is an effect monad, basically gives us access to the methods in MonadError too.
Async doesn't seem to extends MonadError...
Does Async have MonadError instances available regardless of what F is?
Currently I've got something very akin to javascripts "callback hell", and there has to be a better way
I tried for example to use Either and map through assuming that the right bias will help, but it seems map keeps the value within the IO context
so I've still got to do the standard unwrapping
let me show you the terrible code I've managed to cobble together
def registerIntegration(req: Request[IO], auth: String) = {
// First check that we have the correct payload
req
.as[RegisterIntegrationPayload]
.option
.flatMap({
case None => BadRequest("Malformed request body")
case Some(payload) => {
// Check that the user referenced exists
repository
.getUser(payload.userId)
.flatMap({
case None => BadRequest("No user found")
case Some(_) => {
// Unwrap the lightning auth header
authStringToLightningAuth(auth) match {
case Left(st) => BadRequest(st)
case Right((user, pass)) => {
// Make sure we have the correct authentication
LightningAdServer
.getAccount(user, pass)
.flatMap({
case Left(error) =>
InternalServerError(
s"Lightning ad server failed: $error"
)
case Right(accountName) => {
// Mark that the user is lightning registered
repository
.markUserLightningRegistered(payload.userId)
.flatMap(registered =>
if (registered)
Ok("Registered for lightning integration")
else
InternalServerError(
"Failed to register for lightning integration"
)
)
}
})
}
}
}
})
}
})
}
it seems to me that I should be able to avoid this amount of identation in idiomatic scala/cats
but, I've no idea how :/
Use
EitherT or OptionT
(make sure to just use one, like convert all
Eithers into Option or vice versa)
And then remember that
foo.flatMap(x => x.bar.flatMap(y => ???)) is the same as foo.flatMap(x => x.bar).flatMap(y => ???)
i.e. you can always unnest
flatMap calls.
The
for syntax may help with that.
Hi guys, I'm playing with Cats Fibers and having hard time to find some information regarding the integration of Fibers and JVM NIO; specifically do Fibers block when calling NIO operations or are they somehow integrated with such calls and automatically poll/select on file/socket descriptors?
Or is such construct orthogonal to Fibers and user needs to provide such functionality?
Hi guys, for the past two days, I've iterated my code by times. I find a simple way to do something like macwire in cats use IO or Resource. First it only works in Scala3. Finally I choose cats-effect-cps, It becomes more maintainable and intuitive. And than we can do the same thing in zio.RIO, zio.ZManaged, Future because the support of cats-effect-cps. I organized my code on macwire issue Further in Scala3.2 it can be
Hey, I'm having some weird issues with my application just completely locking up after some time. It's all cats effect 3.3.13 (http4s server that makes calls to some old-school blocking apis [keycloak client wrapped with IO.interuptibleMany]). What I observed is that I seem to loose all cats-effect compute threads (io-compute). At the beginning I have two, then some compute-blocker in addition, then when it works I consistently see only the io-scheduler and no other io-* threads..
1 reply
@homycdev hey, you may get more help in Discord but check the resources and examples I have here: https://github.com/pslcorp/programs-as-values
I have cats-core version 2.8.0 as a dependency in my project, and have the import cats._
but my IDE still could not find the Id Monad
I'm trying to use parReduceMapA on a List[Set[MyType]] where MyType has a Semigroup instance defined for it, but I'm getting the error:could not find implicit value for parameter T: cats.Reducible[List]
The code is using tagless final, so it looks kinda like this
object MyService {
def impl[F[_]: Spawn: Parallel]: MyService[F] = new MyService[F] {
private def otherFunc(param1: String, param2: Set[MyType]): List[Set[MyType]] = ???
def myFunc(param1: String, param2: Set[MyType]): F[List[Set[MyType]]] =
for {
myVal <- otherFunc(param1, param2).parReduceMapA(Applicative[F].pure)
... etc
Okay, figured this out: List can be empty, so requires a Monoid, and parFoldMapA operates on the Monoid instance, which is why that works and parReduceMapA does not work because it requires a non-empty container since it operates on Semigroup