- wait(?Pid, -Status) is det
- Wait for a child to change status. Then report the child that
changed status as well as the reason. If Pid is bound on entry
then the status of the specified child is reported. If not, then
the status of any child is reported. Status is unified with
exited(ExitCode) if the child with pid Pid was terminated by
calling exit() (Prolog halt/1). ExitCode is the return status.
Status is unified with signaled(Signal) if the child died due to
a software interrupt (see kill/2). Signal contains the signal
number. Finally, if the process suspended execution due to a
signal, Status is unified with stopped(Signal).