Excerpts from Richard W.M. Jones's message of Fri Mar 21 16:06:40 +0100 2008:
> I'm trying to translate Sylvain Le Gall's gettext module to use camlp4
> from ocaml 3.10.0.  The module is a printer which folds over the AST
> looking for certain types of function call by name.  A simplified
> version is shown below.
> 
> This program is supposed to look for all instances of a function named
> f applied to a string.
> 
> I cannot for the life of me work out how to get this to compile.  I've
> tried about a dozen different variations of the module names, 'open',
> 'include' etc. and got a dozen different errors.

You where very close to something working...

Essentially three errors:

> ----------------------------------------------------------------------
> module Id = struct
>   let name = "pr_gettext" 
>   let version = "$Id$" 
> end 
> 
> module Make (Syntax : Camlp4.Sig.Syntax)

Here  it's  Camlp4.Sig.Camlp4Syntax otherwise types are abstract and you don't
have access to constructors.

>   : Camlp4.Sig.Printer(Syntax.Ast).S =
> struct
>   module Loc = Syntax.Loc
>   module Ast = Syntax.Ast
> 
>   class visitor = object
>     inherit Ast.fold as super
> 
>     val t = []
>     method t = t
> 
>     method expr = function
>     | <:expr@loc< f $str:singular$ >> ->

Here you bind loc but don't use it, however that's just a warning.

>       let t = str :: t in

Here the variable is singular not str.

>       {< t = t >}
> 
>     | e -> super#expr e
>   end
> 
>   let print_interf ?input_file ?output_file _ = ()
> 
>   let print_implem ?input_file ?output_file ast =
>     let visitor = (new visitor)#str_item in
>     let t = (visitor ast)#t in
>     List.iter prerr_endline t
> end
> 
> (* Register the new printer. *)
> module M = Camlp4.Register.Printer(Id)(Make) 

And  here it's Camlp4.Register.OCamlPrinter because Camlp4.Register.Printer is
too abstract.

I attach three working versions of it.

To compile them I use

  ocamlbuild -tags camlp4of,use_camlp4 pr_gettext.cmo

The  first  [1]  is  very  closer  to yours. However you don't really define a
proper  printer here prerr_endline, so if the goal is just to iterate over the
AST [2] is a simpler version.

But  why  make  an effect while one can easily go one step further and produce
an OCaml output that define the list of strings to be translated [3].

Cheers,

[1]: pr_gettext.ml
[2]: pr_gettext_simple.ml
[3]: pr_gettext_simple2.ml

-- 
Nicolas Pouillard aka Ertai