This is a part of the
struct module in the
tcllib distribution.
The doc for this command will joyfully be found at
http://core.tcl.tk/tcllib/doc/trunk/embedded/www/tcllib/files/modules/struct/graph.html
Use this to create and manipulate directed graph objects.
[anyone have examples of when to use this?]
The companion package
struct::graphop provides a number of graph algorithms.