graph library for OCaml

 Ocamlgraph is a graph library for OCaml. Its contribution is
 three-fold:
 .
  * It provides an easy-to-use graph data structure together with
    several operations and algorithms over graphs. It is a
    reasonably efficient imperative data structure for directed
    graphs with vertices and edges labeled with integers.
 .
  * Then ocamlgraph provides several other graph implementations
    for those not satisfied with the one above. Some are
    persistent (imutable) and other imperative (mutable). Some
    are directed and other are not. Some have labels for
    vertices, or labels for edges, or both. Some have abstract
    types for vertices. etc.
    These implementations are written as functors: you give the
    types of vertices labels, edge labels, etc. and you get the
    data structure as a result.
 .
  * Finally, ocamlgraph provides several classic operations and
    algorithms over graphs.
    They are also written as functors i.e. independently of the
    data structure for graphs. One consequence is that you can
    define your own data structure for graphs and yet re-use all
    the algorithms from this library -- you only need to provide
    a few operations such as iterating over all vertices, over
    the successors of a vertex, etc.