functor DFS(  eqtype Vertex type Graph 
              val adj: Graph -> Vertex -> Vertex list
) = struct
type Vertex = Vertex type Graph = Graph
fun reachable g s =
let fun member [] _ = false
      | member (h :: t) v = (h = v) 
                            orelse member t v

    fun dfs []        visited = visited
      | dfs (x :: xs) visited =
          if member visited x then dfs xs visited
          else dfs (adj g x @ xs) (x :: visited)
 in
    dfs [s] []
end
end