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

[Jun Inoue <jun.lambda@gmail.com>]

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