[Caml-list] Legality of using module types from .mli in .ml

[Caml-list] Legality of using module types from .mli in .ml

[Thorsten Ohl]

I'm often referring to module types defined in an interface file in
order to reduce redundancy.  For example

    $ cat a.mli
    module type T = sig val n : int end
    module M : T

    $ cat a.ml
    module type T = A.T
    module M : T = struct let n = 42 end

where T can be rather long.  Is this legal?  The manual says in
section 6.12

    A compilation unit behaves roughly as the module definition
    module unit-name : sig  unit-interface end =  struct unit-implementation end 

and refrains from defining `roughly' :-).  I came up with conflicting
evidence:

O'Caml accepts it
    
    $ ocamlopt a.mli a.ml 

However, it is not equivalent to

    module B :
      sig
	module type T = sig val n : int end
      end =
      struct
	module type T = B.T
	module M = struct let n = 42 end
      end
    
which is obviously rejected by O'Caml, since B.T is not bound.  The
pair (a.mli, a.ml) more closely resembles

    module Aux_C =
      struct
	module type T = sig val n : int end
      end
    
    module type C =
      sig
	module type T = Aux_C.T
	module M : T
      end
    
    module C : C =
      struct
	module type T = Aux_C.T
	module M = struct let n = 42 end
      end

without binding Aux.T.  My question is now: is the pair (a.mli, a.ml)
intentionally legal or do I need to expand the reference A.T, as in

    $ cat pedantic_a.mli
    module type T = sig val n : int end
    module M : T

    $ cat pedantic_a.ml
    module type T = sig val n : int end
    module M : T = struct let n = 42 end

because I've have taken advantage of a bug in the compiler.

The reason I'm asking this, is that my shorthand [as in (a.mli, aml)]
breaks Julien Signoles' defunctorizer.

Cheers,
-Thorsten
-- 
Thorsten Ohl, Physics Dept., Wuerzburg Univ. -- ohl@physik.uni-wuerzburg.de
http://theorie.physik.uni-wuerzburg.de/~ohl/     [<=== PGP public key here]
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[Caml-list] Re: Legality of using module types from .mli in .ml

[Julien Signoles]

Thorsten Ohl wrote:
> 
> I'm often referring to module types defined in an interface file in
> order to reduce redundancy.  For example
> 
>     $ cat a.mli
>     module type T = sig val n : int end
>     module M : T
> 
>     $ cat a.ml
>     module type T = A.T
>     module M : T = struct let n = 42 end
> 
> where T can be rather long.  Is this legal?

For me, your module type declaration should be illegal in a.ml. But the
ocaml compiler accepts it... 
So, is it an ocaml bug ? Orelse what is the exact semantic of (.mli,
.ml) ?
 
> The reason I'm asking this, is that my shorthand [as in (a.mli, aml)]
> breaks Julien Signoles' defunctorizer.

The previous example doesn't break my defunctorizer :

	$ ocamldefun --version
	1.02
	$ ocamldefun a.mli a.ml
	$ cat a.ml
	module type T = A.T
	module M = struct let n = 42 end

That's ok (normal because a.mli is still in the ocamldefun environment
when a.ml is defunctorized)...
Can you report me your example breaking my defunctorizer ?

Cheers,
Julien Signoles.

-- 
mailto : Julien.Signoles@lri.fr ; http : www.lri.fr/~signoles
"In theory, practice and theory are the same, 
but in practice they are different" (Larry McVoy)
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[Caml-list] Re: Legality of using module types from .mli in .ml

[Thorsten Ohl]

Julien Signoles <Julien.Signoles@lri.fr> writes:

> The previous example doesn't break my defunctorizer :
> 
> 	  $ ocamldefun --version
> 	  1.02
> 	  $ ocamldefun a.mli a.ml
> 	  $ cat a.ml
> 	  module type T = A.T
> 	  module M = struct let n = 42 end
> 
> That's ok (normal because a.mli is still in the ocamldefun environment
> when a.ml is defunctorized)...

The O'Caml compiler will later not be able to resolve A.T if you use
the `-d' option:

    ohl@wptx47:~misc$ ocamldefun -v
    1.02
    ohl@wptx47:~misc$ cat a.mli
    module type T = sig val n : int end
    module M : T
    ohl@wptx47:~misc$ cat a.ml 
    module type T = A.T
    module M : T = struct let n = 42 end
    ohl@wptx47:~misc$ ocamldefun -d defun a.mli a.ml
    ohl@wptx47:~misc$ cd defun/
    ohl@wptx47:~defun$ ls
    a.cmd  a.ml
    ohl@wptx47:~defun$ cat a.ml
    module type T = A.T
    module M = struct let n = 42 end
    ohl@wptx47:~defun$ ocamlopt a.ml
    File "a.ml", line 1, characters 16-19:
    Unbound module type A.T

I could ignore appendix B of the manual and create a a.cmi:

    ohl@wptx47:~defun$ cp ../a.mli . 
    ohl@wptx47:~defun$ ocamlc a.mli
    ohl@wptx47:~defun$ ocamlopt a.ml

but I'm not supposed to do that, am I?

BTW: given the (currently) uncertain semantics, I have started to
remove the construct from my applications.
-- 
Thorsten Ohl, Physics Dept., Wuerzburg Univ. -- ohl@physik.uni-wuerzburg.de
http://theorie.physik.uni-wuerzburg.de/~ohl/     [<=== PGP public key here]
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[Caml-list] Re: Legality of using module types from .mli in .ml

[Julien Signoles]

>     ohl@wptx47:~misc$ ocamldefun -v
>     1.02
>     ohl@wptx47:~misc$ cat a.mli
>     module type T = sig val n : int end
>     module M : T
>     ohl@wptx47:~misc$ cat a.ml
>     module type T = A.T
>     module M : T = struct let n = 42 end
>     ohl@wptx47:~misc$ ocamldefun -d defun a.mli a.ml
>     ohl@wptx47:~misc$ cd defun/
>     ohl@wptx47:~defun$ ls
>     a.cmd  a.ml
>     ohl@wptx47:~defun$ cat a.ml
>     module type T = A.T
>     module M = struct let n = 42 end
>     ohl@wptx47:~defun$ ocamlopt a.ml
>     File "a.ml", line 1, characters 16-19:
>     Unbound module type A.T
> 
> I could ignore appendix B of the manual and create a a.cmi:
> 
>     ohl@wptx47:~defun$ cp ../a.mli .
>     ohl@wptx47:~defun$ ocamlc a.mli
>     ohl@wptx47:~defun$ ocamlopt a.ml
> 
> but I'm not supposed to do that, am I?

Effectively, you're not supposed to do that (except if you're sure that
the problem of the appendix B cannot be appear in your program).

Julien Signoles.
-- 
mailto : Julien.Signoles@lri.fr ; http : www.lri.fr/~signoles
"In theory, practice and theory are the same, 
but in practice they are different" (Larry McVoy)
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Re: [Caml-list] Re: Legality of using module types from .mli in .ml

[David Brown]

On Wed, Jan 15, 2003 at 06:37:33PM +0100, Julien Signoles wrote:
> >     ohl@wptx47:~misc$ ocamldefun -v
> >     1.02
> >     ohl@wptx47:~misc$ cat a.mli
> >     module type T = sig val n : int end
> >     module M : T
> >     ohl@wptx47:~misc$ cat a.ml
> >     module type T = A.T
> >     module M : T = struct let n = 42 end
> >     ohl@wptx47:~misc$ ocamldefun -d defun a.mli a.ml
> >     ohl@wptx47:~misc$ cd defun/
> >     ohl@wptx47:~defun$ ls
> >     a.cmd  a.ml
> >     ohl@wptx47:~defun$ cat a.ml
> >     module type T = A.T
> >     module M = struct let n = 42 end
> >     ohl@wptx47:~defun$ ocamlopt a.ml
> >     File "a.ml", line 1, characters 16-19:
> >     Unbound module type A.T
> > 
> > I could ignore appendix B of the manual and create a a.cmi:
> > 
> >     ohl@wptx47:~defun$ cp ../a.mli .
> >     ohl@wptx47:~defun$ ocamlc a.mli
> >     ohl@wptx47:~defun$ ocamlopt a.ml

Would it no work to

  ~misc$ ocamlc -c a.mli
  ~misc$ cd defun/
  ~misc$ ocamlopt -c -I .. a.ml

Dave Brown
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