Method walk

chapter19/src/main/java/com/seaofnodes/simple/node/Node.java:614–619

( Function<Node,E> pred )

    // Utility to walk the entire graph applying a function; return the first
    // not-null result.
    final public <E> E walk( Function<Node,E> pred ) {
        assert CODE._visit.isEmpty();
        E rez = _walk(pred);
        CODE._visit.clear();
        return rez;
    }

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