On Fri, Oct 23, 2009 at 6:14 PM, Marc de Falco <marc.defalco@gmail.com> wrote:
> I don't know the exact rule, but I guess that on the right-hand side of a
> let rec defining a ground value named foo you can only write a term which
> evaluates to a finite ground term on the currently defined variables + foo.
> That is to say something that evaluates to a finite tree of constructors
> with
> constants or defined variables as leaves.
> Maybe someone more knowledgeable could state the exact rule.

You can find this in the documentation :
http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#toc70

> P.S. : the code using Obj is far from a solution as it modifies the existing
> structure
> of the list to add cycling and thus, breaks persistency.

Well, you can easily copy the list before using Obj, wich preserves persistency.

Here is a relevant discussion on the list :
http://groups.google.com/group/fa.caml/browse_frm/thread/9aa32076b03dd6ff?pli=1

You can also look at Matias Giovannini's articles on his blogs (wich
are recommended reading anyway) :
http://alaska-kamtchatka.blogspot.com/2007/11/unsafe-clasp.html
http://alaska-kamtchatka.blogspot.com/2007/11/more-elegant-necklace.html