Method walk

chapter18/src/main/java/com/seaofnodes/simple/node/Node.java:633–638

( Function<Node,E> pred )

    // not-null result.
    private static final BitSet WVISIT = new BitSet();
    final public <E> E walk( Function<Node,E> pred ) {
        assert WVISIT.isEmpty();
        E rez = _walk(pred);
        WVISIT.clear();
        return rez;
    }

    private <E> E _walk( Function<Node,E> pred ) {
        if( WVISIT.get(_nid) ) return null; // Been there, done that