Recursive Variant problem..

[Charles Bouillaguet <Charles.Bouillaguet@crans.org>]

Hello Caml-List,

I would like to write a type which describe some kind of term in a  
toy programming language. It has sets, but not sets of sets

type 'a array_ = [`Array of 'a]
type base_sort = [`Int | `Float | `Object | `Array of base_sort]  (*  
arrays of arrays are OK *)
type sort = [base_sort | `Set of  
base_sort]                                  (* sets of sets are NOT OK*)

The problem appear when I want to define my values :

type 'sort array_state = 'sort * [`ArrayStateVar of string |  
`ArrayWrite of 'me  * 'sort base_value * [`Int] base_value * 'sort  
base_value] as 'me
and 'sort base_value = 'sort * [`Inert of unit | `FieldRead of  
[`Object] base_value * 'sort field | `ArrayRead of 'sort array_state  
* ('sort array_) base_value * [`Int] base_value]
and 'sort field = 'sort * [`FieldVar of string | `FieldWrite of 'me *  
[`Object] base_value * 'sort base_value] as 'me

is refused with error :
=========================
In the definition of base_value, type
[ `Int ] array_state
should be
'a array_state
======================

I then have two questions :

a) is it possible to write that with polymorphic variants, and how ?
b) Is it possible to wrote that with Recursive modules, and how ?

I'm CC-ing my classmate Romain (Hi, Romain !), as he may be  
interested...

Charles Bouillaguet
-=-=-=-=-
Ens de Cachan, Currently visiting MIT.