When you need to format a graph, you specify the nodes to be in the graph and the scheme for organizing them. The CLIM graph formatter does the layout automatically, obeying any constraints that you supply.
You can format any graph in CLIM. The CLIM graph formatter is most successful with directed acyclic graphs ( DAG ). "Directed" means that the arcs on the graph have a direction. "Acyclic" means that there are no loops in the graph.
Here is an example of such a graph:
Based on that information, CLIM lays out the graph for you. You can specify a number of options that control the appearance of the graph. For example, you can specify whether you want the graph to grow vertically (downward) or horizontally (to the right). Note that CLIM's algorithm does the best layout it can, but complicated graphs can be difficult to lay out in a readable way.
See 17.5, Advanced Topics for the graph formatting protocol.
Common Lisp Interface Manager 2.0 User's Guide - 3 Mar 2015