How to visualize/draw automata in ocaml?

Question

I am doing composition of automata. So at the end of that, I want to draw the composed automata also. So are there any libraries for that in ocaml? or are there ocaml wrappers written for any graph visualization tool? I have googled for it but didn't get much for ocaml. Any comments on ocamlgraph? I will get more than 100 states in composed automata.

Answer 1

Use ocamlgraph -- it is a graph library that can generate a dot/graphviz file for you but can also do a lot of other stuff that maybe interesting for handling your automata. The library can do fixpoints, spanning trees, graph search, find strongly connected components, etc., etc.

Here is a complete example of some directed graph with labeled edges + module for doing depth-first-search + module for creating dot-representations of it:

(* representation of a node -- must be hashable *)
module Node = struct
   type t = int
   let compare = Pervasives.compare
   let hash = Hashtbl.hash
   let equal = (=)
end

(* representation of an edge -- must be comparable *)
module Edge = struct
   type t = string
   let compare = Pervasives.compare
   let equal = (=)
   let default = ""
end

(* a functional/persistent graph *)
module G = Graph.Persistent.Digraph.ConcreteBidirectionalLabeled(Node)(Edge)

(* more modules available, e.g. graph traversal with depth-first-search *)
module D = Graph.Traverse.Dfs(G)

(* module for creating dot-files *)
module Dot = Graph.Graphviz.Dot(struct
   include G (* use the graph module from above *)
   let edge_attributes (a, e, b) = [`Label e; `Color 4711]
   let default_edge_attributes _ = []
   let get_subgraph _ = None
   let vertex_attributes _ = [`Shape `Box]
   let vertex_name v = string_of_int v
   let default_vertex_attributes _ = []
  let graph_attributes _ = []
end)

with that you can write your program; e.g. something like this:

(* work with the graph ... *)
let _ =
   let g = G.empty in
   let g = G.add_edge_e ...
   ...
   let file = open_out_bin "mygraph.dot" in
   let () = Dot.output_graph file g in
   ...
   if D.has_cycle g then ... else ...

Answer 2

I would just write automata as text to file (in format suitable for graphviz) and then run graphviz against that file.