steps to reproduce:

library(simmer)
send(trajectory(), character(0))

this causes the entire R session to crash.

however, assigning send() to a variable works fine, e.g.

t <- send(trajectory(), character(0))

but then running print(t) will cause the session to crash. running send with a value works fine

send(trajectory(), "abc")

and running this works fine

simmer() |>
  add_generator("x", send(trajectory(), character(0)), at(0)) |>
  run()