gvpr 如何克隆图的边?

How can gvpr clone a graph's edges?

我希望下面的 GraphViz gvpr 命令会复制图形的边,但它只复制它的节点。克隆图形边的正确咒语是什么?

$ echo 'digraph { john -> mary }' | gvpr 'E {clone($O, $)}'
digraph gvpr_result {
        john;
        mary;
}

可以将边正确地克隆到新图中。

BEGIN { graph_t g = graph("new", "D") }  // Initialize new directional graph
E { clone(g, $) }                        // Clone edge into new graph
END { write(g) }                         // Write new graph