From: Yaron Minsky <yminsky@gmail.com>
To: Jacques Le Normand <rathereasy@gmail.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] A limitation of "with type" declarations for first-class modules
Date: Tue, 20 Sep 2011 16:10:57 +0800 [thread overview]
Message-ID: <CADKNfhJbZ9EmrVsL3k8uOaYX7wVSJToN5YuQhpR5w0Ydazc60A@mail.gmail.com> (raw)
In-Reply-To: <CAK0y-35JNF-5z=fj3t+79QVWmE5J-1UpT2dmBqCf6h87Ymx+Eg@mail.gmail.com>
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I agree this works around the limitation, but it does beg the question: why
is the limitation there in the first place?
On Tue, Sep 20, 2011 at 4:00 PM, Jacques Le Normand <rathereasy@gmail.com>wrote:
> first post! let's see if anyone can do better...
>
> module type Foo = sig type t end
> module type Bar = sig type foo_t module Foo : Foo type t = foo_t end
>
> (* compiles *)
> let g (type a) (m : (module Foo with type t = a)) = ()
>
> (* fails to compile with a syntax error *)
> let f (type a) (m : (module Bar with type foo_t = a)) = ()
>
>
> On Tue, Sep 20, 2011 at 3:36 AM, Yaron Minsky <yminsky@gmail.com> wrote:
> > For some reason, 1st-class modules have more restrictive "with" syntax,
> > which turns out to be a practical problem.
> >
> > The main constraint is that with constraints do not seem to be able to
> refer
> > to sub-modules. Consider the following code snippet:
> >
> >> module type Foo = sig type t end
> >> module type Bar = sig module Foo : Foo end
> >>
> >> (* compiles *)
> >> let g (type a) (m : (module Foo with type t = a)) = ()
> >>
> >> (* fails to compile with a syntax error *)
> >> let f (type a) (m : (module Bar with type Foo.t = a)) = ()
> >
> > Of course, ordinary modules have no such constraint. Any thoughts as to
> > what is going on here, and whether it can be fixed? This has really
> > restricted designs I've been using, forcing me to flatten out structures
> > that are more naturally nested.
> >
> > y
> >
>
>
> --
> Caml-list mailing list. Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
>
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next prev parent reply other threads:[~2011-09-20 8:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-20 1:36 Yaron Minsky
2011-09-20 8:00 ` Jacques Le Normand
2011-09-20 8:10 ` Yaron Minsky [this message]
2011-09-20 9:03 ` Alain Frisch
2011-09-20 9:23 ` Jacques Le Normand
2011-09-20 10:07 ` Yaron Minsky
2011-09-20 10:13 ` Yaron Minsky
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