Re: [Caml-list] Problem with class method and polymorphic variants

[Khoo Yit Phang <khooyp@cs.umd.edu>]

Hi,

Thanks for the quick response! I've encountered another strange one  
that may be related. The code below compiles only if you remove the  
underscore in the method "_a". The error message is similar to the  
earlier one, but I think it's a different problem?

class ['a] node d =
     object
         method _d : 'a = d
         method p (x : 'a) = "<data>"
     end

class ['a] pnode data =
     object (self)
         inherit ['a] node data
         (* doesn't compile with the underscore in "_a" *)
         method _a = self
         method p = function `P p -> p#name
     end

Yit
June 25, 2008

On Jun 24, 2008, at 11:12 PM, Jacques Garrigue wrote:

> From: Khoo Yit Phang <khooyp@cs.umd.edu>
>> Hi,
>>
>> I discovered that the attached snippet of Ocaml does not compile in
>> ocamlc, but does work in the ocaml toplevel (tested in v3.10.0 and
>> 3.10.2). Removing anything (except the :int annotation) causes the
>> error to go away. Is it a bug in the type-checker?
>>
>> # cat polymorphic-variants-methods-bug.ml
>> class ['a] c (a : 'a) =
>>    object (s)
>>        method s = s
>>        method d : int = match a with `A b -> b#num
>>    end
>
> Of course this is a bug. I added it myself to the bug tracker.
> By the way you could also trigger it in the toplevel by giving
> explicitly a module signature (this is what ocamlc does internally).
>
> This is now fixed in CVS, branch release310.
> Note that you may still have other kinds of problems using
> upper-bounded polymorpic variants inside constraints. Just report them
> as you go...
>
> Cheers,
>
> Jacques Garrigue