Frédéric Gava wrote:
> Hi,
> 
> I have done a comparaison on three data structures of the stdlib of OCaml (I
> do parallel implementation of this data structure) and I find that the
> module Map does not contain any function for counting the number of elements
> of the data structure:
>    Set, cardinal: t -> int
>    Hashtbl,  lenght : ('a,'b) t -> int
>    Map,    you have to do   "let length the_map = fold (fun _ _ i -> i+1)
> the_map 0 "
> 
> And Set and Hastbl have also fold...
> 
> Is there an explanation (or is it just a missing ;-) ) ?

There is a 'fold' function in functor Make.
val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b

so :

let cardinal e = fold (fun _ _ x -> succ x) e 0;;