Unimplemented modules as top-level signatures

Unimplemented modules as top-level signatures

[Lauri Alanko]

A minor annoyance in OCaml is that although you can (and must) put
each top-level module into its own file, there is no corresponding
mechanism for defining module types on their own: you always have to
put a "module type" definition inside another module, which
complicates scoping, and with standard tools adds an extra level of
indentation to the signature definition.

However, with 3.12 there is solution of sorts: write the signature
definition in foo.mli without an accompanying foo.ml, and then refer
to the signature as "module type of Foo".

Is this horrible style? Are there some pitfalls I should be aware of?
Or are there better solutions to my desire to avoid nested scoping?
Top-level functors would also be nice to have... :)


Lauri Alanko
la@iki.fi

Re: [Caml-list] Unimplemented modules as top-level signatures

[Lukasz Stafiniak]

Interesting question. Lack of response on the mailing list means
agreement that this is an OK style?

On Fri, Dec 17, 2010 at 10:19 AM, Lauri Alanko <la@iki.fi> wrote:
> A minor annoyance in OCaml is that although you can (and must) put
> each top-level module into its own file, there is no corresponding
> mechanism for defining module types on their own: you always have to
> put a "module type" definition inside another module, which
> complicates scoping, and with standard tools adds an extra level of
> indentation to the signature definition.
>
> However, with 3.12 there is solution of sorts: write the signature
> definition in foo.mli without an accompanying foo.ml, and then refer
> to the signature as "module type of Foo".
>
> Is this horrible style? Are there some pitfalls I should be aware of?
> Or are there better solutions to my desire to avoid nested scoping?
> Top-level functors would also be nice to have... :)

[Caml-list] Re: Unimplemented modules as top-level signatures

[Sylvain Le Gall]

Hello,

On 23-12-2010, Lukasz Stafiniak <lukstafi@gmail.com> wrote:
> Interesting question. Lack of response on the mailing list means
> agreement that this is an OK style?
>

I don't think so. Right now:
1) 3.12 is not yet used by everyone
2) its new features are still studied (at least by me)
3) style is really a matter of taste
4) it is in the language, so no problem using it

So basically, go on, test it and give us your feedback. I doubt there
are thousand people already using this, so you will define yourself
what is right or wrong...

AFAIC, I think it is great and that you should use it.

> On Fri, Dec 17, 2010 at 10:19 AM, Lauri Alanko <la@iki.fi> wrote:
>> A minor annoyance in OCaml is that although you can (and must) put
>> each top-level module into its own file, there is no corresponding
>> mechanism for defining module types on their own: you always have to
>> put a "module type" definition inside another module, which
>> complicates scoping, and with standard tools adds an extra level of
>> indentation to the signature definition.
>>
>> However, with 3.12 there is solution of sorts: write the signature
>> definition in foo.mli without an accompanying foo.ml, and then refer
>> to the signature as "module type of Foo".
>>
>> Is this horrible style? Are there some pitfalls I should be aware of?
>> Or are there better solutions to my desire to avoid nested scoping?
>> Top-level functors would also be nice to have... :)
>
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>

Regards,
Sylvain Le Gall