[Caml-list] Polymorphic Variants and Objects

[Caml-list] Polymorphic Variants and Objects

[Jim Farrand]

Take a look at the following OCaml class type definition:

class type foo =
  object
    method bar: [ `A | `B ] 
  end

I want to be able to relax the type of bar so that it can return any variant 
tag, rather than being limited to `A or `B.

Is this possible?  I tried

class type foo =
  object
    method bar: [> ] 
  end

but this is rejected on the grounds that

The method bar has type [> ] where .. is unbound

Any suggestions?

Regards,
Jim
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Re: [Caml-list] Polymorphic Variants and Objects

[Jacques Garrigue]

From: Jim Farrand <jim@farrand.net>

> Take a look at the following OCaml class type definition:
> 
> class type foo =
>   object
>     method bar: [ `A | `B ] 
>   end
> 
> I want to be able to relax the type of bar so that it can return any variant 
> tag, rather than being limited to `A or `B.

What about:

class type ['a] foo =
  object
    constraint 'a = [> `A | `B]
    method bar : 'a
  end

Since you want the variant to be polymorphic, you have to bind its
variable somewhere.

---------------------------------------------------------------------------
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac.jp
		<A HREF=http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>
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Re: [Caml-list] Polymorphic Variants and Objects

[Jim Farrand]

On Thursday 20 December 2001 02:07, Jacques Garrigue wrote:

> Since you want the variant to be polymorphic, you have to bind its
> variable somewhere.

Thanks, that's exactly what I needed to know.

Regards,
Jim
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