(quasi FAQ) object, variants, .... Unbound type parameter [..]

[Basile STARYNKEVITCH <basile@starynkevitch.net>]

Hello All,

I'm a bit ashamed to ask such a quasi FAQ, but I don't understand why
the following does not compile


  class virtual ['VarT,'NodeT] myclass = object(self)
    method virtual v : 'VarT
    method virtual n : 'NodeT
  end;;

  type 
    'a vart = [> `NothingV | `IntegerV of int | `NodeV of 'a nodet ]
  and
    'a nodet = Empty | LeafI of int | ObLeaf of 'a instancet | Node of nodet list
  and
    'a instancet = ('a,nodet) myclass constraint 'a = 'a vart


I'm getting the following error

File "ess.ml", line 8, characters 12-66:
Unbound type parameter [..]

which is positionned inside the bracket [] of vart line.

Sorry for asking such a nearly FAQ; I thought that this would be a
nearly canical example of the use of constraint.

The real context of all this is some scriptable Wiki-like application
which contains a (dynamically typed) interpreter (quasi scheme
semantics with some ml-like or ada-like syntax). The actual need is to
box in an open variant type (like vart above) all the "special" values
of the interpreter.


Again, my apologies for asking a nearly FAQ... (I googled a bit, but
did not understood the relation between the answers & my question).

Regards

-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile<at>starynkevitch<dot>net 
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