ludic/examples/events/recurse.ludic

# recurse.ludic — EV6: re-entrant emit is bounded. Ping's listener emits Pong,
# Pong's listener emits Ping — an event cycle that would hang the frame forever.
# The depth bound (EV_DEPTH_CAP) makes the nesting trap as an early return, so the
# program terminates with a bounded count instead of spinning. This is the "no
# runaway event cycle" guarantee.
#
# Running it prints:  16   (the cycle bottoms out at the depth cap, deterministically)
program Recurse {
  state RecurseState {
    n: int = 0
  }

  event Ping { }
  event Pong { }

  @On(Ping) handler A(recurse_st: mut RecurseState) { recurse_st.n += 1; emit Pong() }   # each Ping deepens by one Pong
  @On(Pong) handler B { emit Ping() }              # ...and each Pong by one Ping

  entry (recurse_st: RecurseState) {
    emit Ping()
    print(recurse_st.n)
  }
}