Re: [Caml-list] Type That's Concrete From Within A Library Abstract From Without

[Elie Canonici Merle <elie.canonicimerle@gmail.com>]

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Hi,

Do you need to expose that B.t and A.t are the same?

Because if you don't it works.

$ cat > a.ml
type t = Foo of int
let x : t = Foo 3
$ cat > b.ml
type t = A.t
let x2 = A.x
$ cat > p.mli
module B : sig type t val x2 : t end
$ ocamlc -for-pack P -c a.ml b.ml
$ ocamlc -c p.mli
$ ocamlc -pack -o p.cmo a.cmo b.cmo

If you need to expose the type equality you can make it work by adding the
signature of the module A while still keeping A.t abstract in p.mli (or
not, depending on your needs)

$ cat > a.ml
type t = Foo of int
let x : t = Foo 3
$ cat > b.ml
type t = A.t
let x2 = A.x
$ cat > p.mli
module A : sig type t end
module B : sig type t = A.t val x2 : t end
$ ocamlc -for-pack P -c a.ml b.ml
$ ocamlc -c p.mli
$ ocamlc -pack -o p.cmo a.cmo b.cmo

I hope it helps.


2018-04-27 10:53 GMT+02:00 Jun Inoue <jun.lambda@gmail.com>:

> Hi Jacques,
>
> OCaml gives a type error if a public type in b.ml references a
> non-trivial type in a.ml.  Is there a way around this?
>
> $ cat > a.ml
> type t = Foo of int
> let x : t = Foo 3
> $ cat > b.ml
> type t = A.t
> let x2 = A.x
> $ cat > p.mli
> module B : sig type t = A.t val x2 : t end
> $ ocamlc -for-pack P -c a.ml b.ml
> $ ocamlc -c p.mli
> $ ocamlc -pack -o p.cmo a.cmo b.cmo
> File "_none_", line 1:
> Error: The implementation (obtained by packing)
>        does not match the interface p.mli:
>        In module B:
>        Modules do not match:
>          sig type t = A.t val x2 : A.t end
>        is not included in
>          sig type t = A.t val x2 : t end
>        In module B:
>        Type declarations do not match:
>          type t = A.t
>        is not included in
>          type t = A.t
>
>
> On Fri, Apr 27, 2018 at 3:05 PM, Jacques Garrigue
> <garrigue@math.nagoya-u.ac.jp> wrote:
> > You can provide a mli for the -pack.
> > Just compile it before.
> >
> > $ cat > a.ml
> > type t = int
> > let x : int = 3
> > $ cat > b.ml
> > let x2 = A.x * A.x
> > $ ocamlc -for-pack P a.ml b.ml
> > $ cat > p.mli
> > module A : sig type t val x : t end
> > module B : sig val x2 : int end
> > $ ocamlc -c p.mli
> > $ ocamlc -pack -o p.cmo a.cmo b.cmo
> >
> > Now, if you use your library with only p.cmo and p.cmi available, you
> will
> > only be able to access it through the interface you provided.
> >
> > Also, the method using module aliases can work too: you just have
> > to use longer file names for the internal modules, to reduce the risk of
> > conflicts. But this is more involved than using -pack with a mli.
> >
> > Jacques Garrigue
> >
> > On 2018/04/27 14:48, Jun Inoue wrote:
> >>
> >> Hi Ivan,
> >>
> >> That's basically our current approach, but it doesn't solve the
> >> namespace pollution problem.  In your example, when someone installs a
> >> file named b.cmi (whose interface is unrelated to your b.ml), the name
> >> conflict prevents loading the std.cma file at all:
> >>
> >> $ ocaml
> >>        OCaml version 4.04.0
> >>
> >> # #show B;;
> >> module B : sig val foo : int end
> >> # #load "std.cma";;
> >> The files std.cma and b.cmi disagree over interface B
> >>
> >> So the technique makes B inaccessible but doesn't remove it from the
> >> namespace.  This is why we want to -pack things, because our analogue
> >> of b.ml is named matrix.ml, and there's no other sensible name for it.
> >>
> >> This technique doesn't work with -pack because that option demands all
> >> .cmi's, including b.cmi.  I guess we could rename matrix.ml to
> >> matrix_internal_dont_touch.ml, but we wanted to know if there's a
> >> cleaner approach.  I wish we could supply a .mli file to the product
> >> of -pack, but that also doesn't work...
> >>
> >> On Fri, Apr 27, 2018 at 12:06 AM, Ivan Gotovchits <ivg@ieee.org> wrote:
> >>> Hi Jun,
> >>>
> >>> You can achieve this by implying an extra layer of indirection, i.e.,
> by
> >>> having two levels of interfaces. For example,
> >>>
> >>>   * A.ml - implementation of module A
> >>>   * A.mli - private interface of module A
> >>>   * B.ml  - implementation of module B that may rely on anything in
> A.mli
> >>>   * Std.ml - a set of modules that you would like to import, e.g.,
> `module
> >>> A = A`, `module B = B`
> >>>   * Std.mli - public interface specification
> >>>
> >>>
> >>> Next, you deploy `std.cmxa` and `std.cmi` but keep `a.cmi` and `b.cmi`
> to
> >>> yourself. This will prevent users from accessing your private modules
> A and
> >>> B directly. (In oasis you can use PrivateModules stanza for this)
> >>>
> >>> Now you will have `Std.A` and `Std.B` that exposes as much as you
> want. Not
> >>> sure whether it will work with the `-pack`, but you can use this
> approach
> >>> instead of it. This is how we address the same issue in [BAP][1]
> >>>
> >>> Cheers,
> >>> Ivan
> >>>
> >>> [1]: https://github.com/BinaryAnalysisPlatform/bap
> >>>
> >>>
> >>> On Thu, Apr 26, 2018 at 10:18 AM, Jun Inoue <jun.lambda@gmail.com>
> wrote:
> >>>>
> >>>> Dear list,
> >>>>
> >>>> Is there a way to make a type concrete inside a library, yet opaque to
> >>>> library users, preferably in a way that works with -pack?  This is a
> >>>> nagging issue in our sundials package
> >>>> (http://inria-parkas.github.io/sundialsml/).
> >>>>
> >>>> Basically, we have a type declared in one module of the library that
> >>>> is pattern-matched upon in other modules, like:
> >>>>
> >>>> (* private.ml *)
> >>>> type opaque_type = Foo | Bar
> >>>>
> >>>> (* public.ml *)
> >>>> let f : opaque_type -> int = function
> >>>>  | Foo -> 0
> >>>>  | Bar -> 1
> >>>>
> >>>> There are a few constraints:
> >>>> - We don't want users to be able to pattern-match on opaque_type.
> >>>> - We need multiple modules in the library to pattern-match on
> >>>> opaque-type (so moving opaque_typ e to public.ml is not an option).
> >>>> - To avoid namespace pollution, we want to pack the whole library
> >>>> (with ocamlc -pack) as a single Sundials module, so the user sees a
> >>>> Sundials.Public module instead of just Public.
> >>>>
> >>>> Is this possible?  Right now, we just collect public.cmo and
> >>>> private.cmo into sundials.cma and throw away private.cmi.  But this
> >>>> doesn't work with packing:
> >>>>
> >>>> $ ocamlc -pack -o sundials.cmo private.cmo public.cmo
> >>>>
> >>>> demands that there be a private.cmi.
> >>>>
> >>>> --
> >>>> Jun Inoue
> >>>>
> >>>> --
> >>>> Caml-list mailing list.  Subscription management and archives:
> >>>> https://sympa.inria.fr/sympa/arc/caml-list
> >>>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> >>>> Bug reports: http://caml.inria.fr/bin/caml-bugs
> >
> >
> >
>
>
>
> --
> Jun Inoue
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
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>

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