Hello
Here is the latest Caml Weekly News, for the week of December 05 to 12, 2006.
I've updated the godi package for wyrd to version 1.4.1. Wyrd is a curses-based front-end to remind. The home page is here: http://www.eecs.umich.edu/~pelzlpj/wyrd/
I've had a look at chapter 12 of the O'Rielly book as well as the wrapper for ocaml-fftw3 and cairo-ocaml and it all seems a little daunting. I was wondering if there was any semi-automated too for creating Ocaml bindings for C libraries. Any pointers appreciated.Chris King answered:
I recently discovered that SWIG (http://www.swig.org/) supports O'Caml (though I haven't yet used it myself). If you're looking for speed though it may not be the best choice since all C types are mapped to one variant type in O'Caml. You can find O'Caml-specific docs here: http://www.swig.org/Doc1.3/Ocaml.html I presume you're looking to wrap libsndfile... I've wrapped a few similar libraries manually with very few problems. The libsndfile API looks to me like it should be fairly straightforward to wrap thanks to O'Caml's Bigarrays (plus you'll have lots of cut & paste). Start by writing a few simple integer, string, or array functions for O'Caml in C to get a feel for the API without having to worry about custom blocks and such. The curses wrapper in chapter 18 of the O'Caml manual is also a very good starting point. The custom block from that example can be used nearly verbatim for many C structures (such as SNDFILE *). I can provide you with the source of a couple other small wrappers if you like.Richard Jones also answered:
Obviously there are some semi-automated ways, such as SWIG and camlidl mentioned already. But I would definitely urge you to look at doing the wrapping by hand. It's really not that hard, although you should pay careful attention to ch18 of the manual. Rich. ch18: http://caml.inria.fr/pub/docs/manual-ocaml/manual032.htmlDaniel Bünzli added:
Another way is to meta program the bindings using C macros, especially if many stubs have the same structure, have a look at the file ml_gl.h in lablgl [1]. Daniel [1] http://wwwfun.kurims.kyoto-u.ac.jp/soft/lsl/lablgl.html
I'm working on a SAT solver in OCaml. The solver has various types, like three-valued bools, variables, literals. I have modules that encapsulate these types and the operations on them. Now, as it turns out, all these types are represented as ints, but the other modules that use those types don't need to know that - and as a matter of taste I'd rather not expose this. The signatures of these modules currently contain lines like this: type variable (* = int *) If I uncomment all instances of (* = int *) and reveal the representation to the compiler then I get a ... 36% performance improvement in the SAT solver. I have two questions: 1/ Is there some way I can reveal this representation to the parts of the system that clearly need it for effective optimization, without opening this up for general use. 2/ Failing that, has someone got a pleasant method of doing conditional compilation so that I can switch these comments on and off with ease? I'm using version 3.09.2 of ocamlopt.Chris Stork answered the first question:
http://martin.jambon.free.fr/opaque/Opaque.html seem to be what you're looking for in the particular case of ints.Philippe Wang suggested:
I saw once that there were a lot of optimizations based on types informations, especially on basic types... So hidding some type information would lead to prevent the compiler from some optimization... Well, I wonder about how to hide the information from the users without hiding it to the type checker... Typically the function compare (or other comparison operators) have to check the kinds of their arguments, except when the compiler knows that their types are basic types... Well, I guess you use a lot the function compare ? Have you tried to force the polymorphic functions' types that are only used with integers with the type int ? (to take back the performance, you will have to tell explicitely the compiler to optimise them... or change the compiler code... I guess.)Eric Cooper suggested and Jon Harrop answered:
> You can use > type variable = Variable of int > etc. > in your signatures. > This makes the representation visible for optimization purposes, > incurs no representation overhead, In OCaml, that imposes a huge representation overhead.Andrej Bauer suggested:
You can use multiple signatures and modules to combine things just the
way you want them. For example, you could have modules and signatures
organized as follows (I made up some types which don't really make sense
for SAT):
(** The SAT module as seen from the outside. *)
module type SAT =
sig
module Solver :
sig
type variable (* abstract *)
type problem (* abstract *)
type solution = (variable * bool) list
val solve : problem -> solution
end
module SomethingUseful : sig ... end
end
module Sat : SAT =
struct
(* inside SAT all types are concrete *)
type variable = int
type problem = (variable * variable * variable) array
type solution = (variable * bool) list
module SatHelper =
struct
(* here is a helper module which is not even seen from outside *)
(* it can rely on internal representation *)
let internal_solve = ...
end
(* The module Solver is exported, we put in it exactly what we want
the user to see. *)
module Solver =
struct
type variable = variable
type problem = problem
type solution = solution
let solve = SatHelper.internal_solve
end
module SomethingUseful = struct ... end
end
My point is that by nesting modules and exposing just the right amount
of their interfaces through several different signatures, you can
control precisely what is seen from where. There is no need to always
realy on the simplistic view
module = .ml file
signature = .mli file
which is just a convenient shortcut that works in simple examples.
Best regards,
Andrej
P.S. The example above makes it look as if you have to stick everything
inside one huge file. That's not true, as you can use "include", as well
as type sharing constraints ("with type1 = type2") to expose certain
types between modules.
Nicolas Pouillard also answered:I take the second part of your question since the obvious answer is camlp4: There is an extension called pa_macro that provides conditional compilation. Alas this extension doesn't work with signatures so the following example is not (yet) supported: (* foo.mli *) IFDEF ABSTRACT THEN type t ELSE type t = int ENDIF To address that shortcoming you can write an extension syntax dealing with some semi-opaque types. Such an extension can allow us to write that: (* foo.mli *) type t = semi opaque int And have compilation option to set: # For an abstract version $ ocamlc -c -pp "camlp4o ./pa_opaque.cmo -abstract" foo.mli # For a concrete version $ ocamlc -c -pp "camlp4o ./pa_opaque.cmo -concrete" foo.mli With this extension: -----------8<---------------------------------------------------------- (* pa_opaque.ml *) open Pcaml;; let abstract = ref true;; EXTEND ctyp: [[ LIDENT "semi"; LIDENT "opaque"; t = SELF -> if !abstract then <:ctyp< 'abstract >> else t ]]; END;; Pcaml.add_option "-abstract" (Arg.Set abstract) "Use abstract types for semi opaque ones";; Pcaml.add_option "-concrete" (Arg.Clear abstract) "Use concrete types for semi opaque ones";; -----------8<---------------------------------------------------------- Compiled that way: $ ocamlc -c -I +camlp4 -pp "camlp4o pa_extend.cmo q_MLast.cmo" pa_opaque.ml
At http://www.boblycat.org/~malc/apc/ http://www.boblycat.org/~malc/imt/ http://www.boblycat.org/~malc/icedock/ you can find new versions of (0.96, 1.00, 0.4 respectively): CPU load monitor Microsoft command line utilities helper Window Maker like dock utility APC was ported to Linux/PPC IMT was adjusted to work better with path names with spaces in them IceDock finally works correctly on systems with LSB images. The bug was in excellent XLib by Fabrice Le Fessant and was there forever as far as i can see. XLib was also slightly adjusted so that newer OCaml compilers produce less warning messages.
Just to announce the first release of ocaml-dbus, version 0.01. This is an alpha release (few memory leaks, missing some proper finalize function, and maybe segfault lurking), and the library is quite big so not everything is wrapped. However it should works for basic use, and the test program should be enough to get to know how to use it. project page: http://tab.snarc.org/projects/ocaml_dbus/ direct download link: http://tab.snarc.org/download/ocaml/ocaml_dbus-0.01.tar.bz2
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