: (run-action)  ( tick e -- tick' e' )
                2dup @ = if cell+ dup @ ?dup
                  if execute else nip -1 swap then
                else cell+
                then cell+ ;

: run-loop      ( loop exit'-- )
                >r 0 begin
                  over begin dup @ -1 <> while (run-action) repeat drop
                  standby 1+
                  r@ execute
                until 2drop rdrop ;