The interface aims to make it as generic as possible, so that one does not have to use special data structures to define one's graph edges, instead one provides a set of objects corresponding to graph roots and a function that, when applied to the object corresponding to a node, gives edge information. For those familiar with CLIM's format-graph-from-roots, the interface is somewhat similar.
This is my first shot at an asdf-installable system, and the system is at a very early state (i.e., not at all optimized). On the other hand, this is an algorithm that I find myself regularly needing, so I felt it worth offering.
There is some ALBERT-generated HTML documentation included with the package (oddly, the key all-shortest-paths function doesn't appear on the main package page...).
Download: http://rpgoldman.real-time.com/lisp/floyd-warshall_0.02.tgz
License: LLGPL