now it compiles
but still, can someone explain what this error message means?
object Main extends js.JSApp {
def main(): Unit = {
val rootNode = dom.document.getElementById("playground")
ReactDOM.render(EditableSortableListDemo.c(), rootNode)
frp()
}
def frp()(implicit ctx: Ctx.Owner)={
import rx._
val a = Var(1); val b = Var(2)
val c = Rx{ a() + b() }
println(c.now) // 3
a() = 4
println(c.now) // 6
}
}
still complains
> fastOptJS
[info] Compiling 1 Scala source to /Users/joco/dev/scala.js/react/sjs-playaround/stable/target/scala-2.11/classes...
[error] /Users/joco/dev/scala.js/react/sjs-playaround/stable/src/main/scala/Demo/Main.scala:16: No implicit Ctx.Owner is available here!
[error] frp()
[error] ^
[error] one error found
[error] (compile:compileIncremental) Compilation failed
[error] Total time: 1 s, completed Dec 8, 2016 7:11:06 AM
>
where can i get that implicit ?
this is an issue here too lihaoyi/scala.rx#67
@fdietze I am very new myself and struggling a lot. Also, I've actually not seen
a.update before. The difference between using a.now and a() on the right hand side is that a() can be used only inside reactive context. a.now can be used outside reactive context in which it gives the current value of a and inside reactive context in which it doesn't add a dependency to a from the reactive variable that the context is computing. Contrast this with using a() inside the context which adds a dependency
@SRGOM that makes sense, thank you. The scala compiler provides syntactic sugar for apply() and update(): http://otfried.org/scala/apply.html, so
a() = 5 is exactly the same as a.update(5)
Probably interesting for everyone: I think we have a bit too many reactive dom libraries with the same goals: scala-js/scala-js#2843 What do you think?
The docs don't seem to indicate I need to provide a Ctx in this case. And if I provide one, I'm afraid to override accidentally others that are supposed to be generated by macros at other places. Any hint?
I don't exactly know what's the difference
@fdietze I was just going through your google groups discussion and I would agree with you and say (here, don't want to use google groups) that I understand and partially share your concern. My fear was that scala-js has too little people working relative to the goods it offers and wish that the efforts were in sync. I don't have any numbers on scala-js usage, nor do I know if we're gathering a bigger audience and at what rate, but I would say that if our numbers are increasing then surely I (and I'm guessing you too?) don't mind this explosion since the number in a way legitimizes the existence of scala.js
to be fair, I wrote that before I knew what the functor laws were.. i should probably revisit that code to make sure those things are lawful!
I don’t think this has anything to do with map or functor laws, as replacing map with the corresponding Rx construct leads to the same problem:
import $ivy.`com.lihaoyi::scalarx:0.3.2`, rx._
object Example {
val v1 = Var(0)
val v2 = Rx { v1() }
val v22 = Rx { v1() }
val v23 = Rx { v22() }
val v3 = Rx { v23() }
def q(implicit trackDependency: Ctx.Data) = {
if (v1() == 0) v2()
else {
val b = v3() != v2()
if (b)
103
else
17
}
}
val v = Rx { q }
val list = {
var result = List.empty[Int]
val obs = v.trigger { result = result :+ v.now }
v1() = 1
v1() = 2
result
}
}
println(Example.list)This prints List(0, 103, 17) instead of List(0, 17), too.
Hi,
I've got a problem with calling Futures out of Rx.
Just copy and paste the following code into ScalaFiddle:
import rx._
import rx.async._
import scala.concurrent.Future
import scala.concurrent.Promise
import scala.concurrent.ExecutionContext.Implicits.global
def request(id: Int): Future[String] = {
val p = Promise[String]()
js.timers.setTimeout(500) {
println(s"Request: $id")
p.success(id.toString)
}
p.future
}
val id = Var[Int](0)
val idString = id.flatMap(i => request(i).toRx("..."))
id() = 10
println("End...")And you fall into a loop, with the following output:
End...
Request: 0
Request: 10
Request: 10
Request: 10
Request: 10
Request: 10
Request: 10
Request: 10
etc....Is this a known behaviour? or is this a bug?
Is there a workaround for this kind of pattern?
Thanks for your help.
Roll
@rreckel Yea, currently the way flatMap works, it recreates the inner rx whenever the inner rx changes - this interacts poorly with toRx because, as you see in your test, it throws it in an infinite loop.
Im having a hard time coming up with an alternate definition of toRx that actually works within flatmap and am considering just removing it all together.
So ive been playing around with alternatives, and this seems to work:
implicit class FutureCombinators[T](val v: rx.Rx[Future[T]]) extends AnyVal {
def flatten(initial: T)(implicit ec: ExecutionContext, ctx: Ctx.Owner): Rx[T] = {
var result = Var(initial)
v.foreach { x => x.foreach(result.update) }
result
}
}And its used this way:id.map { x => request(x) }.flatten("...")
@rreckel would something like that work? @fdietze what do you think?
I tried your flatten function:
import rx._
import rx.async._
import scala.concurrent.Future
import scala.concurrent.Promise
import scala.concurrent.ExecutionContext
implicit class FutureCombinators[T](val v: rx.Rx[Future[T]]) extends AnyVal {
def flatten(initial: T)(implicit ec: ExecutionContext, ctx: Ctx.Owner): Rx[T] = {
val result = Var(initial)
v.foreach { x => x.foreach(result.update) }
result
}
}
def request(id: Int): Future[String] = {
val p = Promise[String]()
js.timers.setTimeout(500) {
println(s"Request: $id")
p.success(id.toString)
}
p.future
}
import scala.concurrent.ExecutionContext.Implicits.global
val id = Var[Int](0)
val idString = id.map(i => request(i)) .flatten("...")
val result = for {
i <- id
is <- idString
} yield s"$i -> $is"
result.foreach(println(_))
id() = 10
id() = 20
println("End...")This code generates the following result in ScalaFiddle:
0 -> ...
10 -> ...
20 -> ...
End...
Request: 0
20 -> 0
Request: 10
20 -> 10
Request: 20
20 -> 20This is not exactly what I expected..... but still better than an infinite loop ;-)
What do you think?