class Integrator{
   // continuously integrate a function `K`, at each `interval` seconds'
   fcn init(f,interval=1e-4){
      var _interval=interval, K=Ref(f), S=Ref(0.0), run=True;
      self.launch();  // start me as a thread
   }
   fcn liftoff{ // entry point for the thread
      start:=Time.Clock.timef;  // floating point seconds since Epoch
      t0,k0,s:=0,K.value(0),S.value;
      while(run){
	 Atomic.sleep(_interval);
	 t1,k1:=Time.Clock.timef - start, K.value(t1);
	 s+=(k1 + k0)*(t1 - t0)/2.0; S.set(s);
	 t0,k0=t1,k1;
      }
   }
   fcn sample  { S.value  }
   fcn setF(f) { K.set(f) }
}