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

[Romain Bardou <romain.bardou@inria.fr>]

Le 30/10/2012 15:32, Oliver Bandel a écrit :
>
>
> Am 30.10.2012 um 07:12 schrieb Anton Lavrik<alavrik@piqi.org>:
>
>> Hi Francois,
>>
>> I don't use .mli files that much. Granted, I'm a rather casual OCaml
>> user, but hey, at least you are not alone :)
>>
>> I'm surprised by some of the comments you've received. The fact that
>> some people tend to practice top-down coding more than others doesn't
>> really mean anything. Other people do it differently even regardless
>> of the language they use. For me, paper and pencil are far more useful
>> than .mli files up until the interfaces converge and stabilize.
>>
>> In general, .mli files are useful and even essential for libraries and
>> large projects. For instance, they allow to clearly (and cleanly)
>> define interfaces and help with separate compilation (i.e. to avoid
>> recompiling parts).
>>
>> The biggest inconvenience with .mli files as I see it is that I have
>> to repeat myself and make related but slightly different changes in
>> two places when I change a module implementation. I would very much
>> prefer to declare and document public interfaces next to the
>> implementation and have language tooling take care of separate
>> compilation and documentation generation.
>
>
> ocamlc -i
> is your friend...
>
> Ciao,
>     Oliver
>
>

ocamlc -i is not that useful IMO.

It's not incremental: if you modify a file and want to update the .mli, 
ocamlc -i will not help, because using it directly would remove all 
comments and abstractions.

I don't even find it useful to start a new .mli file, because usually 
when I do that, I don't have the implementation yet.

Even if I have the implementation, so much work will be needed after 
ocamlc -i that it's just easier to start from scratch, write the 
interface that I think I should have, and compare with the existing one. 
It allows to check that what I have implemented is what I actually want.

The work I'm talking about is the following.
- Abstract stuff. This involves removing some values, some types, some 
type definitions, adding "private" keywords, replacing types by their 
abstraction.
- Documentation. This involves writing some ocamldoc and categorizing 
stuff in sections. I know a lot of programmers are lazy and do not put 
ocamldoc in their .mli but this is even more important than the .mli 
itself, IMO.

Related:

http://caml.inria.fr/mantis/view.php?id=5777

Now, it does not mean that nothing could be done. Probably an approach a 
la Pascal, with an "interface" section and an "implementation" section 
in the same file, could be used to avoid some code duplication. But that 
would not help with separate compilation. Maybe ocaml should provide 
something like:

include type t in sig

Which would mean "copy-paste the definition of t from the .mli".

Cheers,

-- 
Romain Bardou