The following blog post might be of use.

   http://ocaml.janestreet.com/?q=node/18

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On Wed, Dec 17, 2008 at 2:45 PM, Jacques Carette <carette@mcmaster.ca>wrote:

> I have two (related) questions:
> 1) Has anyone transcribed the TypeRep library into ocaml?
> http://people.cs.uu.nl/arthurb/dynamic.html
>
> 2) How do I embed 'dynamically known' data into a single ocaml
> data-structure?
>
> More specifically, I am experimenting with a (new) language which allows
> deduction and computations to be performed with equal ease on its terms.
>  This language uses ocaml has the host meta-language (ie the interpreter is
> written in ocaml).  I would like to be able to use arbitrary ocaml
> data-structures to represent some of my terms, when these terms are known to
> come from specific theories.  For example, I would like to use Bigint to
> represent integers, but without exposing that per se.  Perhaps a better way
> to phrase this would be to say that I want to have a "generic external data
> container" type in my language terms, which I can instantiate in multiple
> different ways (in the same program), with data handled in different
> modules, without having to change the 'generic' data-structure everytime I
> add a new module.
>
> Polymorphic variants of course come to mind - but they would force me to
> add a new type parameter to all my types, which I would rather avoid.  I
> would be quite happy to use polymorphic variants if I could 'hide away' the
> extra type parameter involved with open variants.  My attempts at hiding
> this parameter (with existentials) has been too successful, in that once
> hidden I can't extract my data from this container anymore [which is the
> correct behaviour for the compiler].
>
> I thought of using objects too, but my data does not really have any common
> structure, so the object would be a pure container.  I cannot see any
> advantage over polymorphic variants, and all the same headaches of an
> 'extra' polymorphic parameter remain.
>
> Jacques
>
>
>
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