with_restarts(). rst_list() returns the names
of all restarts currently established. rst_exists() checks
if a given restart is established. rst_jump() stops
execution of the current function and jumps to a restart point. If
the restart does not exist, an error is thrown.
rst_maybe_jump() first checks that a restart exists before
jumping.
rst_list()
rst_exists(.restart)
rst_jump(.restart, ..., .args = list())
rst_maybe_jump(.restart, ..., .args = list())with_restarts(), rst_muffle().