[Ocaml-lib-devel] ExtLib 0.1 ExtHash

[Amit D. <adubey@CoLi.Uni-SB.DE>]

> (* ****** Module ExtHash **** *)
> 
> module ExtHash :
>   sig
> 
> 	(* return all the keys of an Hashtable
> 	   if the key is several time in the Hashtable, the list will
> 	   contain it that many times *)
> 	val keys : ('a,'b) Hashtbl.t -> 'a list
> 
> 	(* return all the values of an Hashtable *)
> 	val values : ('a,'b) Hashtbl.t -> 'b list
> 
> 	(* remove all bindings for the given key *)
> 	val remove_all : ('a,'b) Hashtbl.t -> 'a -> unit
> 
>   end

    I use hashtables extensively in my work, and there are
two functions that I find invaluable.  (The names, I admit,
might be stupid :)

(* return the element bound to the given key; if no such
   element exists, return a default value *)

val find_always : ('a,'b) Hashtbl.t -> ~key : 'a -> ~default : 'b -> 'b
val safe_find (* alternate name *)

(* replace an old binding with a new one whose value depends
   on the old one.  If no previous binding exists, use a default
   value
 *)

val update :
    ('a, 'b) Hastbl.t ->
    ~key : 'a ->
    ~default : 'b ->
    ('b -> 'b) -> unit

    My primary use of hashtables is to store sparse arrays, which
assume a value of `0.0' anywhere there is currently no binding.
I'm not sure this is useful to people who don't use hashtables
this way.

    -Amit