Re: [Caml-list] Why should I use .mli files?

[Oliver Bandel <oliver@first.in-berlin.de>]

Am 30.10.2012 um 22:25 schrieb Gabriel Scherer <gabriel.scherer@gmail.com>:

> Independently of this discussion, I have been discussed related issues
> with a friend for the last two weeks. I think there would be a feature
> proposal to make in this area that would be *relatively* natural and
> help solve the following different problems in this area:
> 1. Repeating types, module types and class types declarations in the
> .mli and the .ml is redundant and increases the maintenance burden


Hmhh, not sure if Innserstand whatbyou mean.
But as a mli-file narrows the default signature,
repeating types mustbe done.
An empty mli-file would create an empty signature,
and IMHO thats good.
Otherwise it would be necessary to have another mechanism to
narrow the automatic copying of types.

If I missed your pointm then you need to explain in more depth, what you mean.



> 2. The semantics of type-checking the .ml as a whole, and then
> checking that it matches the .mli signature is sometimes inconvenient:
> checking values against their .mli counterpart could help detect
> typing mistakes sooner, which is helpful to get error messages that
> are easier to understand

What is your argument? pro or contra?
It looks weird to me.


> 3. Some users want to have annotations on values (at least at
> toplevel) for readability and the expression language is not optimal
> for this (in particular the fact that type variables do not enforce
> polymorphism)

??


> 
> ## Proposal
> 
> My suggestion would be to allow two features (the second depending on
> the first):
> 1. allow to insert signature items anywhere in a module structure or
> .ml file, giving a reasonable semantics to it
>    (in particular allow inclusion of signature as a structure item,
> with the derived semantics)


This is something that possibly would create a big mess,
and also seems to mix up interface and implementation
for the module language.
At least thats my fear. Mybe if its well done, it would work.

I just suspect, that something important has been forgotten...






> 2. have a syntax to designate the mli signature from the ml file
> (possible suggestion: "module type", used a signature expression)
> 
> By combining the two features you could have something like
> 
> a.mli
>  type t = A | B of u
>  type u
>  val f : 'a -> 'a
> 
> a.ml
>  include (module type with type u = int)
>  let f x = x

??


> 
> But you could also write only a.ml:
>  type t = A | B of u
>  type u = int
>  val f : 'a -> 'a
>  let f x = x

??


If you don't use mli files, then the exported signiture
is available and is like what you find inside the ml-file.
So what is new here?

I,may missed the point, but you can omit mli-files today also....

Ciao,
   Oliver