From: Xavier Leroy <xavier.leroy@inria.fr>
To: Jakob Lichtenberg <jl@itu.dk>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] ocaml internal representation
Date: Thu, 13 Mar 2003 17:45:59 +0100 [thread overview]
Message-ID: <20030313174559.A1781@pauillac.inria.fr> (raw)
In-Reply-To: <003e01c2e96d$5557a6f0$6401a8c0@redmond.corp.microsoft.com>; from jl@itu.dk on Thu, Mar 13, 2003 at 06:32:10AM -0800
> In O'Caml the types are compiled away, right?
Yes, in a sense, but they are also used to determine memory
representation of data to some extent.
> Then, is there actually a performance/memory overhead in replacing:
> type coord = int * int
> with:
> type coord = Coord of (int * int)
There is no memory overhead with the following two definitions:
type coord = Coord of int * int
type coord = {x:int; y:int}
In both cases, values of type coord will be represented by a two-word
memory block (plus one word of header) holding the two integers --
just like a pair of integers int*int.
However, there *is* some overhead with your proposed
type coord = Coord of (int * int)
that is interpreted as "Coord takes one argument that is a pair",
causing two memory blocks to be used, one for the pair, one for the
application of Coord. In contrast,
type coord = Coord of int * int
instructs the compiler to treat Coord as taking two arguments that are
integers.
> Is it recognized as a 'reasonable' way to get the type system to help me not
> mixing up stuff (except for signatures of course)?
Yes, it's one way to do it. The other is to use abstract types via
signature constraints, as you said.
> Slightly more general: Did I miss any doc. about this in the O'Caml manual?
The chapter "interfacing C with OCaml" contains a *lot* of details on
the data representations used by compiled code. Perhaps more details
than you'd like to know :-)
- Xavier Leroy
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prev parent reply other threads:[~2003-03-13 16:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-13 14:32 Jakob Lichtenberg
2003-03-13 16:45 ` Xavier Leroy [this message]
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