Examples with VoidVisitor kodkod.ast.visitor.VoidVisitor used on opensource projects

Example 1 with VoidVisitor

use of kodkod.ast.visitor.VoidVisitor in project org.alloytools.alloy by AlloyTools.

the class Nodes method minRoots.

/**
 * Returns a minimal subset of {@linkplain #roots(Formula) roots} of the given
 * formula such that all nodes in the given collection are reachable from those
 * roots. The returned subset is a local minimum in that none of its members can
 * be removed without leaving some node in the descendants set unreachable from
 * the remaining roots.
 *
 * @requires descendants in formula.*components
 * @return { s: Set<Formula> | s.elements in roots(formula) and descendants in
 *         s.elements.*components and no s': Set<Formula> | s.containsAll(s')
 *         and s'.size()<s.size() and descendants in s.elements.*components }
 * @throws IllegalArgumentException descendants !in formula.*components
 */
public static Set<Formula> minRoots(Formula formula, Collection<? extends Node> descendants) {
    final Set<Node> desc = new IdentityHashSet<Node>(descendants);
    final VoidVisitor visitor = new AbstractVoidVisitor() {

        final Set<Node> visited = new IdentityHashSet<Node>();

        @Override
        protected boolean visited(Node n) {
            if (visited.add(n)) {
                desc.remove(n);
                return false;
            }
            return true;
        }
    };
    final Set<Formula> roots = new LinkedHashSet<Formula>();
    for (Formula root : roots(formula)) {
        final int size = desc.size();
        root.accept(visitor);
        if (desc.size() < size) {
            roots.add(root);
        }
        if (desc.isEmpty()) {
            break;
        }
    }
    if (!desc.isEmpty())
        throw new IllegalArgumentException("descendants !in formula.*components: formula=" + formula + " ; descendants=" + descendants);
    return roots;
}