Re: Visitor in OCaml [was Re: [Caml-list] C++/C# inheritance is bad?]

["blue storm" <bluestorm.dylc@gmail.com>]

On 1/19/09, Yoann Padioleau <padator@wanadoo.fr> wrote:
> What we want is really give code like
>
> let my_analysis program =
>  analyze_all_expressions program (fun expr ->
>    match expr with
>    | FunCall (e, es) -> do_something()
>    | _ -> <find_a_way_to_recurse_for_all_the_other_cases>
>  )
>
> The problem is how to write analyze_all_expressions
> and find_a_way_to_recurse_for_all_the_other_cases.

You should have a look at the Camlp4 "metaprogramming" facilities :
http://brion.inria.fr/gallium/index.php/Camlp4MapGenerator

You would write something like :
let my_analysis program =
  let analysis = object (self)
    inherit fold as super
    method expr = function
    | FunCall (e, es) -> do_something (); self
    | other -> super#expr other
  end in analysis#expr

While sometimes a bit hairy, the object oriented layer makes it easy
to use a refine mapper or folders without writing all the heavy
plumbing yourself.