Re: [Caml-list] strange error with packed modules and module type of

[Markus Mottl <markus.mottl@gmail.com>]

On Tue, May 29, 2012 at 8:25 PM, Milan Stanojević <milanst@gmail.com> wrote:
> g.mli:
> module Std : sig include module type of Std end

Btw., this is equivalent and slightly shorter:

  module Std : module type of Std

> and compile similarly like before
> ocamlopt.opt -for-pack G -c foo.mli foo.ml
> ocamlopt.opt -for-pack G -c foo.cmx std.ml
> ocamlopt.opt -c g.mli
> ocamlopt.opt -pack -o g.cmx foo.cmx std.cmx
>
> But now I get this helpful error message
[snip]
> Does anyone know what is going on here?

This seemingly identical construction compiles:

g.mli:
module Std : sig module Foo : module type of Foo end

I guess this also points to what is going wrong.  If I understand this
correctly, the workaround basically says: "Std contains a submodule
Foo which just happens to have the same signature as the module
implemented by foo.ml".  But the broken version says: "Std contains a
submodule Foo which is equivalent to the module implemented by
foo.ml".  This equivalence is somehow lost with packing, hence the
unhelpful error message.  Not sure, but I guess this can be fixed in
the compiler?

Regards,
Markus

-- 
Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com