From: Jon Harrop <jon@jdh30.plus.com>
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] 'a Set?
Date: Wed, 26 Jan 2005 09:13:08 +0000 [thread overview]
Message-ID: <200501260913.09018.jon@jdh30.plus.com> (raw)
In-Reply-To: <727068A7-6F2C-11D9-8411-0003939A19AA@fas.harvard.edu>
On Tuesday 25 January 2005 23:54, Mike Hamburg wrote:
> Is there a clean way to do this without removing the code from set.ml
> and modifying it?
I do not believe so. I have also had to do this.
Compared to a flat set of functions, the functor approach has the advantage of
enforcing a consistently used compare function. The same effect can be
achieved with "elt = 'a" by writing a higher-order function which returns a
record containing the Set.* functions using the given function argument as
the compare function. Something equivalent to this:
type 'a t = 'a list
type 'a set =
{ empty : 'a t;
is_empty : 'a t -> bool;
add : 'a -> 'a t -> 'a t;
mem : 'a -> 'a t -> bool }
let rec add compare e = function
[] -> [e]
| h :: t -> match compare h e with
-1 -> e :: h :: t
| 0 -> e :: t
| _ -> h :: add compare e t
let rec mem compare e = function
[] -> false
| h :: t -> match compare h e with
-1 -> false
| 0 -> true
| _ -> mem compare e t
let make ?(compare=compare) () =
{ empty = [];
is_empty = (fun s -> s=[]);
add = add compare;
mem = mem compare }
Possible issues with this are that building closures (i.e. in "make") is
expensive and that the resulting type is monomorphic ('_a). You can probably
get a polymorphic type most easily by putting the definitions of "add" etc.
in the record definition, rather than partially applying their arguments.
Cheers,
Jon.
next prev parent reply other threads:[~2005-01-26 14:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-25 23:54 Mike Hamburg
2005-01-26 8:25 ` [Caml-list] " Jean-Christophe Filliatre
2005-01-26 10:13 ` Frédéric Gava
2005-01-26 11:04 ` Radu Grigore
2005-01-26 12:04 ` Jacques Garrigue
2005-01-26 16:00 ` Alex Baretta
2005-01-26 16:14 ` Jacques Carette
2005-01-26 21:09 ` Mike Hamburg
2005-01-29 9:55 ` Radu Grigore
2005-01-26 9:13 ` Jon Harrop [this message]
2005-01-26 15:36 ` Frédéric Gava
2005-01-26 16:06 ` Jon Harrop
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