implement less defaulty interface in cont.pl

src/prolog/lib/cont.pl

@@ -1,16 +1,19 @@
 
 :- module(cont, [reset/3, shift/1]).
 
-reset(Goal, Cont, Term) :-
+reset(Goal, Ball, Cont) :-
     call(Goal),
     '$reset_cont_marker',
     '$bind_from_register'(Cont, 3),
-    '$bind_from_register'(Term, 4).
+    '$bind_from_register'(Ball, 4).
 
 shift(Term) :-
     '$nextEP'(first, E, P),
     get_chunks(E, P, L),
-    Cont = cont(call_continuation(L)),
+    (  L == [] ->
+       Cont = none
+    ;  Cont = cont(call_continuation(L))
+    ),
     '$write_cont_and_term'(_, _, Cont, Term),
     '$unwind_environments'.