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RE: [Caml-list] strange behaviour with variants and "cannot be g eneralized"
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Date: -- (:)
From: skaller <skaller@o...>
Subject: RE: [Caml-list] strange behaviour with variants and "cannot be g eneralized"
On Wed, 2003-09-10 at 18:18, Jacques Garrigue wrote:
> From: "Beck01, Wolfgang" <BeckW@t-systems.com>

>  In that case we have now polymorphic fields.
>       type mix = {data: 'a. 'a -> 'a ; mutable count: int}
>       let r = {data = (fun x -> x); count = 0}
> 
> So, I think this is a good idea in itself, but before I try again
> introducing this improvement, I need a few compelling examples to
> justify the effort.

Curious: this isn't yet dual to the variants: the field values
are polymorphic, by the record itself is not. Wouldn't one like
to have a record of a set of tags where the typing is like:

	match { `A 1; `B 2 } with
	| { `A x } -> ...

that is, allow subtyping based on tag sets?
[Hmm .. what is the variance of the field values ?]

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