Could you give some simplified example that can be ran? From the error message
it's the line `next.callback = (proc() {.closure, gcsafe.})(cb0)` that gives
the error.Very likely the next object type doesn't have any defined proc with that or you missed some module (which I don't know which) Also, is that `ptr[Msg[T]]` typo? Afaik, you should write it like this: `ptr Msg[T]`
