Running a simple Scala.React expression - scala

Question

I am looking into Scala.React, and the updated paper on the issue, trying to get a simple Signal based example to work.
I understand that the Signal method in the paper doesn't exist as such, but instead there are Strict and Lazy. So my naive first attempt:
Setting up the whole thing:
object dom extends scala.react.Domain {
val engine = new Engine
val scheduler = new ManualScheduler
}
import dom._
Trying out composition:
val v1, v2 = Var(0)
val f = Strict { v1() + v2() }
The second line crashes with
java.lang.AssertionError: assertion failed: This method must be run on its domain
scala.react.NilDebug#4eaf6cb1
at scala.Predef$.assert(Predef.scala:179)
at scala.react.Debug.assertInTurn(Debug.scala:37)
at scala.react.EngineModule$Propagator.defer(EngineModule.scala:120)
...
So I must be doing something wrong. But what?
Second attempt:
scala> dom.start()
scala> var v1, v2, f = (null: Signal[Int])
v1: dom.Signal[Int] = null
v2: dom.Signal[Int] = null
f: dom.Signal[Int] = null
scala> schedule { v1 = Var(0); v2 = Var(0) }
scala> schedule { f = Strict { v1() + v2() }}
scala> engine.runTurn()
scala> schedule { println(f.now) }
scala> engine.runTurn()
Uncaught exception in turn!
scala.react.EngineModule$LevelMismatch$

Answer 1

Ok, so first of all we should use Lazy instead of Strict if we want to keep a reference to those signals, because Strict requires to be run within a scheduled turn.
The following is my new attempt. Not sure if this is how it's intended, but it works:
object Test extends scala.react.Domain with App {
val engine = new Engine
val scheduler = new ManualScheduler
val v2 = Var(0)
val v1 = Lazy { v2() + 10 }
val f = Lazy { v1() + v2() }
start()
schedule {
new Observing {
observe(f) { p =>
println(s"Observed: $p")
}
}
v2() = 5
}
runTurn()
}