From: Michael Vanier <mvanier@cs.caltech.edu>
To: martin_jambon@emailuser.net
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] extensible records again
Date: Sun, 21 Mar 2004 01:22:17 -0800 (PST) [thread overview]
Message-ID: <20040321092217.BBA0E9BBA2@orchestra.cs.caltech.edu> (raw)
In-Reply-To: <Pine.LNX.4.40.0403211617410.1400-100000@localhost> (message from Martin Jambon on Sun, 21 Mar 2004 16:53:38 +0800 (HKT))
Interesting. I'll try it. Thanks!
Mike
> Date: Sun, 21 Mar 2004 16:53:38 +0800 (HKT)
> From: Martin Jambon <martin_jambon@emailuser.net>
> Cc: caml-list@inria.fr
>
> On Sat, 20 Mar 2004, Michael Vanier wrote:
>
> > So I tried this. Aside from the pain of having to change data to 'a data in
> > lots of places (which I can live with), I got bitten by the polymorphic
> > reference limitation. Specifically, I have a mutable stack of data values
> > which became a mutable stack of 'a data values, but the function which
> > creates the mutable stack is of type '_a data, so it doesn't type check. I
> > can't figure out any way around this. Basically, my main data type _cannot_
> > be parameterized.
>
> Keep your code polymorphic: create your stack in the same compilation
> unit as the full type instanciation.
> Then you have to pass your stack as a parameter
> to all functions that use it.
>
> I guess this is more or less what you do:
>
> (* a.ml *)
> let stack =
> let st = Stack.create () in
> Stack.push (`Int 1) st;
> st
> (* compiler complains about '_ *)
>
>
> (* b.ml *)
> let some_function x =
> match Stack.pop stack with
> `Int i -> print_int i
> | `Custom s -> print_string s
> | _ -> ()
>
>
> Instead you should write:
>
> (* a.ml *)
> let init_stack () =
> let st = Stack.create () in
> Stack.push (`Int 1) st;
> st
>
>
> (* b.ml *)
> let some_function stack x =
> match Stack.pop stack with
> `Int i -> print_int i
> | `Custom s -> print_string s
> | _ -> print_float x
>
> let _ =
> let stack = A.init_stack () in
> some_function stack 1.2
>
>
> I hope it answers your question...
>
> Martin
>
>
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next prev parent reply other threads:[~2004-03-21 9:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-21 6:21 Michael Vanier
2004-03-21 8:08 ` Oleg Trott
2004-03-21 8:40 ` Michael Vanier
2004-03-21 16:10 ` Oleg Trott
2004-03-21 17:06 ` skaller
2004-03-21 17:36 ` Oleg Trott
2004-03-22 3:19 ` skaller
2004-03-22 7:49 ` Ville-Pertti Keinonen
2004-03-22 9:32 ` Oleg Trott
2004-03-22 10:25 ` Ville-Pertti Keinonen
2004-03-21 22:35 ` Michael Vanier
2004-03-22 3:39 ` skaller
2004-03-21 22:34 ` Michael Vanier
2004-03-22 3:31 ` skaller
2004-03-22 5:54 ` Michael Vanier
2004-03-23 19:14 ` skaller
2004-03-24 1:41 ` Jacques Garrigue
2004-03-24 8:44 ` Julien Signoles
2004-03-24 10:04 ` Jacques Garrigue
2004-03-21 8:53 ` Martin Jambon
2004-03-21 9:22 ` Michael Vanier [this message]
2004-03-21 17:00 ` skaller
2004-03-22 8:13 ` Achim Blumensath
2004-03-23 2:14 ` Michael Vanier
2004-03-23 7:25 ` Achim Blumensath
2004-03-31 10:05 ` Marcin 'Qrczak' Kowalczyk
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