[cwn] Attn: Development Editor, Latest Caml Weekly News

[Alan Schmitt]

Hello,

Here is the latest Caml Weekly News, for the week of 24 to 31  
January, 2006.

1) hints for internationalization
2) On Store_field()

========================================================================
1) hints for internationalization
Archive: <http://thread.gmane.org/gmane.comp.lang.caml.general/32050>
------------------------------------------------------------------------
** Basile Starynkevitch asked and Sylvain Le Gall suggested:

 > Do you have practical hints regarding the l18n or i18n of an  
application
 > (specifically, an application to be runnable either in french or in
 > english)?
 >
 > Any practical hints are welcome. In particular, it seems to me  
that the
 > novel features of the Printf module could help in particular the  
format string
 > substitution eg printf "%(%d %s)" (I don't know what should come  
next) ....
 >
 > In other words, I'm seeking advices and examples of how to use  
advanced
 > Printf (& Scanf) features to code a bi-lingual application.
 >
 > Maybe a Printf mini-HOWTO might be helpful?
 >
 > What about gettext (or other equivalent?)

There is ocaml-gettext, if you need a gettext library.

<http://le-gall.net/sylvain/ocaml-gettext.html>

========================================================================
2) On Store_field()
Archive: <http://thread.gmane.org/gmane.comp.lang.caml.general/31971>
------------------------------------------------------------------------
** Continuing the thread from last week, Thomas Fischbacher said and  
Olivier Andrieu answered:

 > What you *actually* forgot to tell people is that OCaml
 > unfortunately lacks a macro with which one can store C pointers to
 > alloc_final allocated blocks. If one writes to those using e.g.
 >
 >   ml_vector = alloc_final(2, finalize_vector, 1, 10);
 >   Store_field(ml_vector, 1,(value)vector);
 >
 > with vector being a C pointer to a structure, this may or may not
 > lead to random crashes at very unexpected places - because (as I
 > think now) the Store_field macro will be over-eager trying to tell
 > the GC about the value stored - which it should just ignore in this
 > particular case!
 >
 > Indeed, this has been discussed before, I think:
 >
 > <http://groups.google.de/group/fa.caml/msg/60ace9405fcf60c0? 
dmode=source&hl=de>
 >
 > So, I would strongly suggest introducing a macro that behaves like  
this:
 >
 > #define Store_c_field(block,offset,x) (Field(block,offset)=(value)x)
 >
 > so that one could then use
 >
 >   Store_c_field(ml_vector, 1,vector);
 >
 > I actually just spent a full week tracking down precisely this
 > issue in a not particularly trivial C library interface I am
 > building right now.  After looking in the weirdest places, ensuring
 > it's not an issue with the library wrapped, or the trickier pieces
 > of my own code, I even started patching debugging code into the
 > OCaml bytecode's GC and rebuilding...
 >
 > So, *please* do the world a great favour and tell people about that
 > issue in the C interface documentation!

Well, it already does:
,----
| Rule 3   Assignments to the fields of structured blocks must be done
| with the Store_field macro (for normal blocks) or Store_double_field
| macro (for arrays and records of floating-point numbers). Other
| assignments must not use Store_field nor Store_double_field.
`----
Final (aka custom) blocks are not structured blocks but raw blocks
(not traced by the GC), so assignements to those blocks falls in the
"other assignments" category.

A good way to deal with custom blocks in the C code is to create a
small struct type and access the content of the block through this type.

struct custom_foo_bar {
   foo *pointer1;
   bar *pointer3;
};

value alloc_foo_bar (foo *f, bar *b)
{
   value v;
   struct custom_foo_bar *s;
   v = alloc_custom (&foo_bar_ops, sizeof struct custom_foo_bar, 1, 10);
   s = Data_custom_val (v);
   s->p1 = f;
   s->p2 = b;
   return v;
}

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Using folding to read the cwn in vim 6+
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Here is a quick trick to help you read this CWN if you are viewing it  
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vim (version 6 or greater).

:set foldmethod=expr
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zM
If you know of a better way, please let me know.

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

Alan Schmitt, <http://sardes.inrialpes.fr/~aschmitt/>