Alain Frisch wrote:

>>Many thanks! I just had a glance at it, but it seems to be just how one
>>would have to approach such a problem. (The issue with hash-based
>>approaches to find previously visited substructures is that during
>>traversal, a GC may occur. Now I just assume that this may involve
>>relocation and heap compaction in OCaml. The problem then is that
>>OCaml does not properly support what would be known as eq hash tables
>>in Lisp.)
> 
> 
> As long as the data structure supports the polymorphic hash function, it
> should work to simply use a regular hash table with the polymorphic hash
> function and physical equality, as in:
> 
> module S = Hashtbl.Make(struct
>    type t = Obj.t
>    let hash = Hashtbl.hash
>    let equal = (==)
> end);;

Why? (I.e. I'm not convinced yet.)

-- 
best regards,
Thomas Fischbacher
t.fischbacher@soton.ac.uk