1:      1  1 CALL pred list_cmd.main/2-0 (det) list_cmd.m:22
mdb> echo on
Command echo enabled.
mdb> list_cmd ./list_cmd.sh
mdb> step
       2:      2  2 CALL pred list_cmd.fib/2-0 (det) list_cmd.m:29 (list_cmd.m:23)
mdb> list
 27 :- pred fib(int::in, int::out) is det.
 28 
*29 fib(N, F) :-
 30     ( if N < 2 then
 31         F = 1
mdb> continue -n
8