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

["Nicolás Ojeda Bär" <nicolas.ojeda.bar@lexifi.com>]

Sorry, I forgot the last step in my email, which is to create a cma
with all the compilation units:

  ocamlc -a sundials*.cmo -o sundials.cma

and install sundials.cma and the public *.cmi's as needed.

Best wishes,
Nicolás

On Thu, Apr 26, 2018 at 5:03 PM, Nicolás Ojeda Bär
<nicolas.ojeda.bar@lexifi.com> wrote:
> Dear Jun,
>
> This is a limitation of module packs. However, there is a much better
> alternative to module packs in the form of module aliases which will
> allow you to do what you want.
>
> You can head to
> https://caml.inria.fr/pub/docs/manual-ocaml/extn.html#sec249 for a
> more lengthy explanation, but briefly, in your example:
>
> 1. rename private.ml to sundials__private.ml and public.ml to
> sundials__public.ml
> 2. create a file sundials.ml with contents:
>
>   module Private = Sundials__private
>   module Public = Sundials__public
>
> 3. compile sundials.ml with
>
>   ocamlc -no-alias-deps -c sundials.ml
>
> (you may want to disable warning 49 when doing this)
>
> 4. compile the individual files in the library with
>
>   ocamlc -no-alias-deps -open Sundials -c sundials__private.ml
>   ocamlc -no-alias-deps -open Sundials -c sundials__public.ml
>
> 5. You can now delete (or not install) sundials__private.cmi and ship
> the other files
>
>   sundials.cmo
>   sundials.cmi
>   sundials__public.cmo
>   sundials__public.cmi
>   sundials__private.cmo
>
> to hide the private module from "outside" library users.
>
> Note that if you use jbuilder/dune, then your library will be built
> like this (steps 1-4) by default.
>
> Hope it helps,
>
> Best wishes,
> Nicolás
>
> On Thu, Apr 26, 2018 at 4:18 PM, 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
>>
>> --
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