From: Brian Smith <brian-l-smith@uiowa.edu>
To: OCaml Mailing list <caml-list@inria.fr>
Subject: [Caml-list] Polymorphic methods (longest error message ever!)
Date: Sun, 07 Jul 2002 20:25:12 -0500 [thread overview]
Message-ID: <3D28E9F8.5020308@uiowa.edu> (raw)
Hi everybody,
First of all, where can I find some documentation about the CVS versino
of O'Caml? Is the documentation kept in CVS too? Anyway, on to the
problem at hand:
I have a class like this:
class type ['a] node_type =
object
method as_variant : 'a
constraint 'a = [> `Node of 'a node_type]
end;;
class ['a] node : ['a] node_type =
object (self)
method as_variant : 'a = `Node (self :> 'a node_type)
end;;
That works fine in O'Caml 3.04. But, I want to use the new polymorphic
method feature in O'Caml 3.04+15. So I tried:
# class type node_type = object
method as_variant : [> `Node of node_type]
end;;
class type node_type =
object method as_variant : [> `Node of node_type] end
# class node : node_type = object (self)
method as_variant = `Node (self :> node_type)
end;;
^^^^
This expression cannot be coerced to type
node_type = < as_variant : 'a. [> `Node of node_type] as 'a >;
it has type < as_variant : 'c; .. > as 'b but is here used with type 'b
# class node : node_type = object (self)
method as_variant : 'a. [> `Node of node_type] as 'a
= `Node (self :> node_type)
end;;
The class type object method as_variant : [> `Node of node_type] end
is not matched by the class type node_type
The class type object method as_variant : [> `Node of node_type] end
is not matched by the class type
object method as_variant : [> `Node of node_type] end
The method as_variant has type 'a. [> `Node of node_type] as 'a
but is expected to have type 'b. [> `Node of node_type] as 'b
The universal variable 'b would escape its scope
I have no idea what the error message means. To me, it is saying that
class "node" doesn't match class type "node_type" even though everything
has exactly the same type. Could somebody please explain it to me? What
is the correct way of doing the above?
Thanks,
Brian
-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
next reply other threads:[~2002-07-08 1:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-07-08 1:25 Brian Smith [this message]
2002-07-08 2:08 ` John Max Skaller
2002-07-08 2:53 ` Jacques Garrigue
2002-07-09 6:23 ` [Caml-list] Polymorphic methods (syntax) Brian Smith
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3D28E9F8.5020308@uiowa.edu \
--to=brian-l-smith@uiowa.edu \
--cc=caml-list@inria.fr \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).