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Date: Mon, 19 Jan 2009 17:41:35 +0100
From: "blue storm" <bluestorm.dylc@gmail.com>
To: "Yoann Padioleau" <padator@wanadoo.fr>
Subject: Re: Visitor in OCaml [was Re: [Caml-list] C++/C# inheritance is bad?]
Cc: caml-list@yquem.inria.fr
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References: <FCB84B14-903B-4DC9-949E-F4190C6D4873@osu.edu>
	 <200901171327.19141.jon@ffconsultancy.com>
	 <D035AED0-188D-4EF5-BB9A-BE39537B1A70@osu.edu>
	 <200901171659.36732.jon@ffconsultancy.com>
	 <871vuz2rm7.fsf_-_@aryx.cs.uiuc.edu>
X-Spam: no; 0.00; ocaml:01 expr:01 expr:01 camlp:01 camlp:01 storm:98 folders:98 wrote:01 caml-list:01 inherit:01 match:02 inheritance:03 recurse:03 recurse:03 refine:03 

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.