Caml Weekly News

Hello,

Here is the latest Caml Weekly News, week 11 to 18 February, 2003.

1) CamlAgent 0.1
2) Optimizing false polymorphic local functions
3) Any idea about Ocaml 3.07 release date?

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1) CamlAgent 0.1
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SooHyoung Oh announced:

CamlAgent version 0.1
 - Ocaml applications for Microsoft Agent: http://www.microsoft.com/msagent
 - You can see parallel and sequential agent play.
 - Home: http://www.taglib.co.kr/ocaml/camlAgent.html

Requirements:
 * MS agent characters
    - In download page, you can find
       = MS Agent core components
       = MS Agent character files: Genie, Merlin, Peedy, Robby
 * MS Visual C++ Compiler / MS Visual Studio
    - I tested on MS Visual Studio .Net.
 * Ocaml 3.06
 * Lablgtk 1.2.5 - you can source and binary in
  http://wwwfun.kurims.kyoto-u.ac.jp/soft/olabl/lablgtk.html
 * camlidl 1.04
 * camlidl 1.04 patch - I made some patches for MS agent ONLY.

Demos:
 - move: moveSquare, moveCircle
 - hello: parallel, sequential play

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2) Optimizing false polymorphic local functions
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Pascal Zimmer asked and Xavier Leroy answered:

> The other day, I ran into a significant speedup improvement.
> Here is a simpler (and artificial) version:
> 
> let min_list l =
>  let rec loop mini = function
>     [] -> mini
>   | (x::r) -> loop (if x <= mini then x else mini) r
>  in loop max_int l;;
> 
> This function computes the minimal element of an int list. Note however
> that the inner local function "loop" is polymorphic.
> 
> Now consider the slightly different version where "loop" is forced into
> a monomorphic function:
> 
> let min_list l =
>  let rec loop (mini:int) = function
>     [] -> mini
>   | (x::r) -> loop (if x <= mini then x else mini) r
>  in loop max_int l;;
> 
> On my computer in native code, the speedup is really significant: more
> than 6 times faster (OK this example was built on purpose...). The
> reason is that in the first case, the operator <= is replaced by a call
> to the internal polymorphic compare_val function, whereas is the second
> case a direct comparison between integers is performed.
> Note also that if you replace the "if" statement by "min x mini", you
> don't get any speedup because the polymorphic function "min" is called
> in any case.
> 
> I suspect there are other cases in which the compiler can produce a
> better code when it knows more precisely the types involved. 

Yes: besides comparisons, array and bigarray accesses can be compiled
more efficiently if the exact types of the data are known statically.

> So my question is: would it be possible to help him in this way by
> enforcing the type checker to infer a monomorphic type in such  
> situations ? By "such situations", I mean: local polymorphic
> functions that are used in exactly one monomorphic setting
> afterwards. Of course, this is not desirable for global functions,
> since it may break the calculus; but for local functions, it should 
> be of no harm since we know all the places where they are used, and
> it would not change the type of the wrapper, thus being transparent
> for the user...
> Any comment ?

The following paper formalizes exactly this idea, and gives a type
inference algorithm that avoids unecessary polymorphism like you suggest:

  http://citeseer.nj.nec.com/bjorner94minimal.html

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3) Any idea about Ocaml 3.07 release date?
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Alessandro Baretta wondered and Xavier Leroy answered:

> I am wondering whether the Ocaml team has any idea about the 
> next release date. Any ideas?

Certainly not before late April, and hopefully no later than early July.
I can't be any more precise than this at the moment.

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Old cwn
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======================================================================

Alan Schmitt

-- 
The hacker: someone who figured things out and made something cool happen.