From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
To: malc@pulsesoft.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Records typing
Date: Wed, 13 Nov 2002 19:08:42 +0900 [thread overview]
Message-ID: <20021113190842B.garrigue@kurims.kyoto-u.ac.jp> (raw)
In-Reply-To: <Pine.LNX.4.44.0211131250130.567-100000@home.oyster.ru>
From: malc <malc@pulsesoft.com>
> > # module M = struct type t = float and r = {f:t} end;;
> > # module M' = struct type t = float type r = {f : t} end;;
> >
> > In the first case, the record is represented as an array of a pointer
> > to a boxed float, while in the second case it is represented as an
> > array of an unboxed float. Since the data representation is different,
> > these two signatures are not equivalent. I was afraid there would be
> > no direct way to express the first case, but actually you can.
>
> What exactly triggered the switch from boxed to unboxed repersentation?
> I mean, this is completely unobvious and can have severe performance
> degradation, so description of cases when this might happen could be
> useful.
This the use of "and". In mutually recursive type definitions, other
types are not "known" during the definition, and as a result their
representation cannot be used for optimization. I think this is true
for all ocaml releases, but it is specified nowhere, and could be
wrong.
Since you're not going to write the first defintion anyway, this
shouldn't be a real problem.
The real problem is that when you use a signature like
sig type t type r = {f:t} end
in a functor, then this signature cannot be instanciated by the
unboxed version of r when t = float. And there is no way to solve it
short of inlining functors.
Cheers,
Jacques Garrigue
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next prev parent reply other threads:[~2002-11-13 10:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-06 12:57 malc
2002-11-11 11:43 ` Andreas Rossberg
2002-11-13 1:11 ` Jacques Garrigue
2002-11-13 2:41 ` Jacques Garrigue
2002-11-13 14:48 ` Andreas Rossberg
2002-11-13 9:55 ` malc
2002-11-13 10:08 ` Jacques Garrigue [this message]
2002-10-24 10:55 ` Christophe Raffalli
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