Re: [Camllist] sorting Hashtbl.t
 Brian Rogoff
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Date:   (:) 
From:  Brian Rogoff <bpr@a...> 
Subject:  Re: [Camllist] sorting Hashtbl.t 
Brian Rogoff writes: > John Max Skaller writes: > > > From an algorithmic point of view, there is no way to sort an > > > hash table since there is no order attached to items. > [...snip extended Hashtbl interface ...] > > Of course I can write this > > function myself, it's just inconvenient to have to > > keep doing so. Sorry to follow up on my own message, but there is a way to do this kind of extension exactly once with only a tiny bit of clunkiness that I had missed when I wrote the original flawed approach yesterday. So, I still disagree that we need to provide module interfaces for things like hash tables, though it's probably no harm to do so if lots of people agree that such functions do belong in a basic interface. Thanks for making me think about this! First, we create an extra signature in either the .ml and .mli files or in a third (.mli) file, like so (* hashtbl_sig.mli *) module type S = sig type ('a, 'b) t = ('a, 'b) Hashtbl.t val create : int > ('a, 'b) t val clear : ('a, 'b) t > unit val add : ('a, 'b) t > 'a > 'b > unit val copy : ('a, 'b) t > ('a, 'b) t val find : ('a, 'b) t > 'a > 'b val find_all : ('a, 'b) t > 'a > 'b list val mem : ('a, 'b) t > 'a > bool val remove : ('a, 'b) t > 'a > unit val replace : ('a, 'b) t > 'a > 'b > unit val iter : ('a > 'b > unit) > ('a, 'b) t > unit val fold : ('a > 'b > 'c > 'c) > ('a, 'b) t > 'c > 'c end this signature exists just to remove the offending Make from the include, and to create the type equality. The rest is easy (* exthash.mli *) include Hashtbl_sig.S (* Remove the functorial interface *) (* Module extension part *) val elements : ('a, 'b) t > 'b list module type S = sig include Hashtbl.S val elements : 'a t > 'a list end module Make (H : Hashtbl.HashedType) : S with type key = H.t (* exthash.ml *) include (Hashtbl : Hashtbl_sig.S) let elements ht = let r = ref [] in (Hashtbl.iter (fun _ y > r := y::(!r)) ht; !r) module type S = sig include Hashtbl.S val elements : 'a t > 'a list end module Make (H : Hashtbl.HashedType) : S with type key = H.t = struct module Hashtbl = Hashtbl.Make(H) include Hashtbl let elements ht = let r = ref [] in (Hashtbl.iter (fun _ y > r := y::(!r)) ht; !r) end  Brian  To unsubscribe, mail camllistrequest@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/camlbugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners