Re: [Caml-list] Warnings opening modules (was: why is building ocaml hard?)

[Jeremy Yallop <yallop@gmail.com>]

On 15/07/2016, Yotam Barnoy <yotambarnoy@gmail.com> wrote:
> On Jul 15, 2016, at 3:26 PM, Hezekiah M. Carty <hez@0ok.org> wrote:
> > On Fri, Jul 15, 2016 at 2:58 PM Yotam Barnoy <yotambarnoy@gmail.com> wrote:
> > > > On Jul 15, 2016, at 2:09 PM, Jeremy Yallop <yallop@gmail.com> wrote:
> > > > > On 15 July 2016 at 17:57, Yotam Barnoy <yotambarnoy@gmail.com> wrote:
> > > > > In haskell, I can just say 'import A (foo, bar, baz, t)' to limit
> > > > > exactly what I want to import. This is because haskell has a
> > > > > half-baked module system that isn't nearly as powerful as OCaml's,
> > > > > which allows it to create syntax that doesn't need to go anywhere but
> > > > > at the toplevel.
> > > > >
> > > > > We need this functionality in OCaml, but the closest thing is to say
> > > > > 'include struct let foo = A.foo let bar = A.bar let baz = A.baz type t
> > > > > = A.t end'
> > > >
> > > > This can be written more succinctly:
> > > >
> > > >   let foo, bar, baz = A.(foo, bar, baz)
> > > >   type t = A.t
> > >
> > > Ok I have to admit that's pretty convenient.
> > >
> > type t = M.t does not bring M.t's constructors into scope.  ppx_import (
> > https://github.com/whitequark/ppx_import) can help with this if you don't
> > mind preprocessing.
>
> That's a great point. Without that last bit of functionality, this isn't
> really a solution to the problem.

The Haskell example you gave:

   import A(T)

doesn't bring T's constructors into scope, either; it needs to be
written like this:

   import A(T(..))

In OCaml you can bring A.t's constructors into scope by repeating the
definition:

   type t = A.t = T of int