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As a pair of predicates, one for nodes, one for edges: :- pred asg_nodes(asg, node). :- mode asg_nodes(in, out) is nondet. :- mode asg_nodes(in, in) is semidet. :- pred asg_edges(asg, node, node). :- mode asg_edges(in, out, out) is nondet. :- mode asg_edges(in, in, in) is semidet. Underlying are traditional sets or what-have-you but you never have to deal with these at high levels of coding. You could then do fancy stuff like defining ancestry as: :- pred asg_ancestor(asg, node, node). :- mode asg_ancestor(in, out, out) is nondet. :- mode asg_ancestor(in, in, in) is semidet. asg_ancestor(ASG, A, A). asg_ancestor(ASG, A, B) :- asg_edge(A, C), asg_ancestor(C, B). Of course you'd want to wrap this stuff up in a typeclass or some such and give them useful names. |