From: Fabrice Marchant <fabricemarchant@free.fr>
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Building a Set module for elements of a Map
Date: Fri, 27 Jun 2008 20:10:01 +0200 [thread overview]
Message-ID: <20080627201001.7cc5d751@free.fr> (raw)
In-Reply-To: <20080625153043.3bd7895c@free.fr>
Thanks for the useful and interesting answers !
Jean-Christophe Filliâtre explained:
> Using Pervasives.compare instead of a user-defined comparison function
> may even be incorrect. (Suppose the intended comparison function should
> identify (x,y) and (y,x), for instance; obviously, Pervasives.compare
> will not.)
Your clearly exposed things with this example. I suspected my trial was not perfect. I now understand it is erroneous.
> A possible solution to your problem is to have functor F taking instead
> a module for keys as argument, and then to build module M inside F; thus
> it would look like:
>
> module F(K : OrderedType) = struct
> module M = Map.Make(K)
> module MKeySet = Set.Make(K)
> ...
> end
I wanted to extend the functionalities of the Map module. Your solution perfectly suits what I need :
module MapPlus(K : Map.OrderedType) = struct
module M = Map.Make(K)
include M
module MKeySet = Set.Make(K)
let of_list l = List.fold_left (fun a (x, y) -> M.add x y a) M.empty l
let domain map = M.fold (fun k _ -> MKeySet.add k) map MKeySet.empty
end
module StringMap = MapPlus.MapPlus( String )
let sm =
StringMap.of_list ["one", 1;
"two", 2;
"three", 3]
let print l = Printf.printf "{%s}" (String.concat ", " l)
let _ =
print (StringMap.MKeySet.elements (StringMap.domain sm))
(* -> {one, three, two} *)
Xavier Leroy wrote :
> Yet another alternative is to parameterize F over both a Map and a Set,
> adding a sharing constraint to ensure that they work on compatible
> data types:
>
>module F (M: Map.S) (MKeySet: Set.S with type elt = M.key) = struct
> ...
>end
I discover ! Never have thought we could use 'with type elt' constraint this way.
----------------------------------------------------------------
So you cleanly solved the problem to get the domain set of a map.
Please how would you build the module MValSet to express the range set of a map ?
( Inside MapPlus module, by :
let range map = M.fold (fun _ v -> MValSet.add v) map MValSet.empty
)
Regards,
Fabrice
prev parent reply other threads:[~2008-06-27 20:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-25 13:30 Fabrice Marchant
2008-06-26 9:21 ` [Caml-list] " Jean-Christophe Filliâtre
2008-06-26 9:26 ` Xavier Leroy
2008-06-27 18:10 ` Fabrice Marchant [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20080627201001.7cc5d751@free.fr \
--to=fabricemarchant@free.fr \
--cc=caml-list@yquem.inria.fr \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).