add meta_predicate declaration for must_succeed/1
@@ -5884,9 +5884,11 @@ difference_arcs([V|Vs], FL0) -->
writeln(T) :- write(T), nl.
+:- meta_predicate must_succeed(0).
+
must_succeed(G) :-
( G -> true
- ;write(failed-G), halt
+ ; throw(failed-G)
).
enumerate([], _) --> [].
