]> Hugo Ferreira wrote: > Hello, > > I have the following definition: > > module rec H : > sig > type 'a node = > | Node of 'a node J.t > | Leaf of 'a > > type 'a t = 'a node > val equal : 'a t -> 'a t -> bool > val hash : 'a t -> int > end = > struct > type 'a node = > | Node of 'a node J.t > | Leaf of 'a > > type 'a t = 'a node > let equa = (==) > let hash = Hashtbl.hash > end > > and J : Hashtbl.S with type 'a key = 'a H.node = Hashtbl.Make( H ) > ;; > > The data type 'a node is polymorphic. It is also a key used by the > hash-table. Note that H now does not comply with Hashtbl.HashedType > (because Hashtbl.HashedType is not polymorphic). By adding the > constraint "with type" also does not help. > > Is it possible to make H comply with Hashtbl.HashedType i.e: make > J.Key = 'a H.node ? I just posted an implementation of polymorphic hash tables with physical comparison, using the Obj module: http://martin.jambon.free.fr/phys.html It is the following code: (***** phys.mli *****) type ('a, 'b) t val add : ('a, 'b) t -> 'a -> 'b -> unit val clear : ('a, 'b) t -> unit val copy : ('a, 'b) t -> ('a, 'b) t val create : int -> ('a, 'b) t val find : ('a, 'b) t -> 'a -> 'b val find_all : ('a, 'b) t -> 'a -> 'b list val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c val iter : ('a -> 'b -> unit) -> ('a, 'b) t -> unit val length : ('a, 'b) t -> int val mem : ('a, 'b) t -> 'a -> bool val remove : ('a, 'b) t -> 'a -> unit val replace : ('a, 'b) t -> 'a -> 'b -> unit (***** phys.ml *****) (* This implementation uses the Obj module which allows to transgress the type system. It is not regular OCaml. *) module Magic_key = struct type t = Obj.t let equal = ( == ) let hash = Hashtbl.hash end module Magic_table = Hashtbl.Make (Magic_key) type ('a, 'b) t = 'b Magic_table.t let add tbl k v = Magic_table.add tbl (Obj.repr k) v let clear tbl = Magic_table.clear tbl let copy tbl = Magic_table.copy tbl let create n = Magic_table.create n let find tbl k = Magic_table.find tbl (Obj.repr k) let find_all tbl k = Magic_table.find_all tbl (Obj.repr k) let fold f tbl accu = Magic_table.fold (Obj.magic f) (Obj.magic tbl) accu let iter f tbl = Magic_table.iter (Obj.magic f) (Obj.magic tbl) let length tbl = Magic_table.length tbl let mem tbl k = Magic_table.mem tbl (Obj.repr k) let remove tbl k = Magic_table.remove tbl (Obj.repr k) let replace tbl k v = Magic_table.replace tbl (Obj.repr k) v (*****************) Martin -- http://mjambon.com/