:- module(topsort,
[topsort/2]).
:- use_module(library(dgraphs),
[dgraph_new/1,
dgraph_add_edges/3,
dgraph_add_vertices/3,
dgraph_top_sort/2
]).
/* simple implementation of a topological sorting algorithm */
/* graph is as Node-[Parents] */
topsort(Graph0, Sorted) :-
mkedge_list(Graph0, EdgeList, []),
mkvertices_list(Graph0, VList, []),
dgraph_new(DGraph0),
dgraph_add_vertices(DGraph0, VList, DGraph1),
dgraph_add_edges(DGraph1, EdgeList, DGraph2),
dgraph_top_sort(DGraph2, Sorted).
mkvertices_list([]) --> [].
mkvertices_list([V-_|More]) --> [V],
mkvertices_list(More).
mkedge_list([]) --> [].
mkedge_list([V-Parents|More]) -->
add_edges(Parents, V),
mkedge_list(More).
add_edges([], _V) --> [].
add_edges([P|Parents], V) --> [P-V],
add_edges(Parents, V).
