module F = struct
        type source_object = string
        type target_object = string
        let string_of_source_object s = s
        let string_of_target_object s = s
        let target_of s = s ^ ".o"
        let build t =
          print_string ("build "^t^"\n"); flush stdout;
          ignore(Unix.system ("touch "^target_of t))
        ;;
        let mtime_of_source_object s = 
          try Some (Unix.stat s).Unix.st_mtime
          with Unix.Unix_error (Unix.ENOENT, "stat", f) when f = s -> 
            prerr_endline ("Source file not found: "^s);assert false
        ;;
        let mtime_of_target_object t = 
          try Some (Unix.stat t).Unix.st_mtime
          with Unix.Unix_error (Unix.ENOENT, "stat", f) when f = t -> None
        ;;
end

module M = Make.Make(F)

let deps = [
  "a.c", [ "b.c"; "d.c" ];
  "b.c", [ "c.c"; "d.c" ];
  "c.c", [];
  "d.c", ["e.c"];
  "e.c", [];
  ]
;;

M.make deps;;