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From: Brian Hurt <bhurt@spnz.org>
To: "Michael D. Adams" <mdmkolbe@gmail.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Efficency of varient types
Date: Sat, 26 Nov 2005 23:45:03 -0600 (CST)	[thread overview]
Message-ID: <Pine.LNX.4.63.0511262336031.24132@localhost.localdomain> (raw)
In-Reply-To: <c62c8d860511262106g59cb7bccwcfa24124b97a0a2b@mail.gmail.com>



On Sun, 27 Nov 2005, Michael D. Adams wrote:

> I agree, which is why it was my hope that OCaml might do some of that
> for me.  Consider a home brew bool type, "type mybool = Mytrue |
> Myfalse".  If the compiler were smart enough, it could represent that
> as an unboxed type.

The compiler is smart enough to do that already- variants without 
associated data are represented as ints.

> From there it might be a small step to
> semi-unboxed types such as the one I started this discussion with,
> "type value = Int of int | Bool of bool | String of string".

The problem here is that the variants take two words- one word which says 
which variant it is, and the second word which is the unboxed int, unboxed 
bool, or pointer to the boxed string.

The problem with unboxing multi-word structures is that this would break 
other things.  For example, consider List.rev:

let rev lst =
     let rec loop accum = function
         | h :: t -> loop (h :: accum) t
         | [] -> accum
     in
     loop [] lst
;;

This function has a type of 'a list -> 'a list.  Unlike C++ templates, 
Ocaml only generates one copy of this function that works on all types. 
This is because all the list elements fit into a single word- either their 
unboxed types that fit into a single word (int, boolean, char), or the 
members of the list are just pointers to the real (boxed) data.

Brian


  reply	other threads:[~2005-11-27  5:39 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-11-25 23:53 Michael D. Adams
2005-11-26  0:31 ` [Caml-list] " Nicolas Cannasse
2005-11-26  1:22   ` Brian Hurt
2005-11-26  9:39     ` Nicolas Cannasse
2005-11-28  0:17     ` Obj or not Obj Christophe Raffalli
2005-11-28  8:41       ` [Caml-list] " Nicolas Cannasse
2005-11-28  9:27         ` Christophe Raffalli
2005-11-28  9:33         ` skaller
2005-11-28  8:43       ` Alain Frisch
2005-11-26  2:54   ` [Caml-list] Efficency of varient types skaller
2005-11-27  5:06   ` Michael D. Adams
2005-11-27  5:45     ` Brian Hurt [this message]
2005-11-27 10:02       ` Nicolas Cannasse
2005-11-27 15:35       ` Michael D. Adams
2005-11-27 18:08         ` Brian Hurt
2005-12-02 15:07           ` Michael D. Adams
2005-11-26  1:18 ` Jon Harrop
2005-11-27 14:57 ` Lukasz Stafiniak
2005-11-27 15:47   ` Lukasz Stafiniak
2005-11-28  8:14   ` Christophe Raffalli
2005-11-28  7:24 ` David Baelde
2005-11-28  7:49   ` Jacques Garrigue
2005-11-28 10:01     ` Jon Harrop
2005-11-28 10:26       ` Luc Maranget
2005-11-28  7:53   ` Ville-Pertti Keinonen
2005-12-01 17:05 ` Stefan Monnier
2005-12-02 15:07   ` [Caml-list] " Michael D. Adams

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