Re: GenerateFold

["Nicolas Pouillard" <nicolas.pouillard@gmail.com>]

On 5/31/07, Joel Reymont <joelr1@gmail.com> wrote:
> What is the proper use of GenerateFold here?
>
> What I'm trying to do is dig into my AST tree, starting with a list
> of statements at the top, to find out if I have any `FunArgDecl bits.
>
> At the top of the AST I have
>
> statement =
>      [
>      | `InputDecls of input_decl list
>      ]
>
> and then
>
> input_decl =
>      [
>      | `InputDecl of id * ty * expr
>      | `FunArgDecl of id * ty * subscript
>      ]
>
> I tried the following approach but it's obviously wrong.
>
> class fold = Camlp4Filters.GenerateFold.generated;;
>
> let is_fun_arg = object
>    inherit fold as super
>    method input_decl x =
>      match super#input_decl x with
>        | `FunArgDecl _ -> true
>        | _             -> false
> end
>
> let is_fun x = is_fun_arg#statement x;;
>

You must use the object itself that is threaded through the traversal
(or use an exception in that simple case).

Something like (not tested).

class fold = Camlp4Filters.GenerateFold.generated;;

let is_fun_arg = object
   inherit fold as super
   val found = false
   method found = found
   method input_decl x =
     match super#input_decl x with
       | `FunArgDecl _ -> {< found = true >}
       | _             -> self
end

let is_fun x = (is_fun_arg#statement x)#found;;



-- 
Nicolas Pouillard