Branch is not repeated after "self join"

[DannyO-dev]

Hello again, I have another question: Why is my branch in this case is not repeated?

library(simmer)
set.seed(123)

controller <- trajectory("Test Path")

elevator <- simmer()

controller <- controller %>%
  log_("Enter trajectory") %>%
  timeout(1) %>%

  branch(
    function() 1 > 0, continue = TRUE,
    trajectory() %>%
      log_("Enter branch") %>%
      join(controller),

    trajectory() %>%
      log_("DUMMY for branch")) %>%

  log_("Leave trajectory")

elevator <-
  simmer("elevator") %>%
  add_generator("Controller_", controller, at(0))

elevator %>% run(until = 10)
0: Controller_0: Enter trajectory
1: Controller_0: Enter branch
1: Controller_0: Enter trajectory

• I would expect another "Enter branch" here ???

  2: Controller_0: Leave trajectory

Thank you in advance and best regards.

[Enchufa2]

Short answer: just don't reference trajectories recursively. Trajectories are built sequentially. If you do that, wherever you insert the join, you are referencing an object that is being built, and copying that intermediate state, so that's not a good idea.

[DannyO-dev]

OK all right. I am looking for a way to call up a trajectory more than once. What would be the right way to do this? I could for example do it like this:

library(simmer)
set.seed(123)

drive <- trajectory("Test Path")
controller <- trajectory("Controller")

elevator <- simmer()

drive <- drive %>%
  log_("Enter trajectory") %>%
  timeout(1) %>%

  branch(
    function() 1 > 0, continue = TRUE,
    trajectory() %>%
      log_(function() {
        paste("Enter branch")
      }),

    trajectory() %>%
      log_("DUMMY for branch")) %>%

  log_("Leave trajectory")

controller <- controller %>%
  branch(
    function() 1 > 0, continue = TRUE,
    trajectory() %>%
      log_(function() {
        paste("Restart branch")
      }) %>%
      join(drive),

    trajectory() %>%
      log_("DUMMY for branch")) %>%
  rollback(1)

elevator <-
  simmer("elevator") %>%
  add_generator("Controller", controller, at(0))

elevator %>% run(until = 10)

Than I would need the branch a second time. Thank you in advance and best regrads

[Enchufa2]

If you want to repeat something, that's a loop, and there's a mechanism for that which doesn't involve recursion: rollback().