Re: [Caml-list] Programming with modules

[brogoff <brogoff@speakeasy.net>]

On Fri, 20 Aug 2004, Brian Hurt wrote:
> On Fri, 20 Aug 2004, Erik de Castro Lopo wrote:
>
> > Hi all,
> >
> > Say I have a module (main.ml) and an interface (main.mli) which
> > defines a type maintype.
> >
> > However, main.ml is getting a little large and I'd like to split
> > some of the functionality out into another file, but still have
> > access to maintype in the new file. Unfortunately, Ocaml doesn't
> > allow mutual dependancies across acoss files.
> >
> > Does anybody have any suggestions on how to get around this?
> >

> More generally, refactor your code.  Find hunks of code which are already
> mostly independent and consider how to make them more independent, so you
> can cut them out into their own modules.  Limit interactions between
> different parts of the code, and develop interfaces for those interactions
> which are necessary.  This actually leads to more maintainable code.

This is very good advice, and I believe you'd get the same advice if you were
programming in Ada, which also has a module system with (parameterized) modules.
In Erik's case, it's the right thing to do. In general, if entities are mutually
dependent they belong in the same module.

There are a few cases where you really do want to support cross module
dependencies, but this seems to be hard to do in a satifactory way. The
issue is made worse IMO by the addition of OO, since class hierarchies,
at least the ones I've used, tend to have more cyclic dependencies.

Whatever became of the mixin approach?

-- Brian

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