From: Jacques Carette <carette@mcmaster.ca>
To: Andreas Rossberg <AndreasRossberg@web.de>
Cc: caml-list@inria.fr
Subject: How do I achiece this, was Re: [Caml-list] Variance problem in higher-order Functors?
Date: Tue, 25 Jul 2006 16:45:20 -0400 [thread overview]
Message-ID: <44C682E0.6040805@mcmaster.ca> (raw)
In-Reply-To: <00ea01c6ae9d$3c459750$15b2a8c0@wiko>
My real question is (and should have been), how do I translate
module type DOMAIN = sig type kind end
type domain_is_field
type domain_is_ring
module Rational = struct type kind = domain_is_field end
module Integer = struct type kind = domain_is_ring end
module DivisionUpdate(D:DOMAIN with type kind = domain_is_field) = struct
(* something only valid with D a field*)
end
module GeneralUpdate(D:DOMAIN) = struct
(* something that always works, for rings and fields *)
end
The behaviour I want should be the same as the first-order applications
module A = DivisionUpdate(Rational) (* OK *)
module B = GeneralUpdate(Rational) (* OK *)
module C = DivisionUpdate(Integer) (* ERROR *)
module D = GeneralUpdate(Integer) (* OK *)
BUT I want to pass all these modules as parameters to a functor. I
don't see how to build the proper type that will work!
[I have read the manuals in depth, Googled around the caml.inria.fr web
site, played around with the implementation, etc to no avail]
In other words, I want to be able to define
module type Trans = functor(U:UPDATE) -> functor(D:DOMAIN) -> sig ... end
but none of my attempts have worked, even though the first-order code
works fine.
I would be happy with a solution that uses polymorphic variants, or
objects, or whatever work. The only thing I can't do is "run-time"
tests, as I have a dozen domains, with more functors and more
constraints floating around, so I really want this to be a type-level
solution. If OCaml had conditional module application, I could use
that, but "expanding" my definitions is not realistic.
Jacques
next prev parent reply other threads:[~2006-07-25 20:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-23 19:58 Jacques Carette
2006-07-23 21:16 ` [Caml-list] " Andreas Rossberg
2006-07-25 20:45 ` Jacques Carette [this message]
2006-07-26 5:16 ` How do I achiece this, was " Jacques Garrigue
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