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Date: Wed, 31 Oct 2012 18:32:33 +0100
From: Tiphaine Turpin <Tiphaine.Turpin@free.fr>
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Subject: Re: [Caml-list] Why should I use .mli files?

I personally find that the most useful of the missing features that have
been addressed here is the ability to write type definitions only once,
when using interfaces (in particular mi files). Type annotations
(especially with explicit polymorphism) are sufficient for the "value
declaration" concern, in my opinion.

Here is another proposal on this type topic : why not change the
semantics of module type inclusion to consider missing types (and module
types as well) as if they were declared with the same definition ? In
other words, a signature S would be a subtype of S' if there exists some
set of type declarations which, if prepended to S, make it have the type
S' in the usual sense ? Exactly as [> `a ] is a subtype of [> `a | `b ]
for polymorphic variants.

I don't know if a sound semantics can be found for such a thing
(especially since type declarations can refer to each other, unlike
tags) but this would definitely be a backward-compatible modification
(which we still may want to enable only with a command-line flag).

Tiphaine