[m-rev.] diff: implement concat_string_list for .NET

[Fergus Henderson]

On 17-Feb-2003, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> On 16-Feb-2003, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> > +	% This type is for strings which may contain embedded null characters.
> > +:- type string_with_0s ---> string_with_0s(string).
> 
> This is wrong. If you define an abstract data type, it must contain not only
> the character array ("string") but also its length.

That would probably be an improvement.  Feel free to make it.

I didn't want to change the structure of the code significantly --
I was effectively just adding some comments, in a way that the
compiler could check.

> > +% This version is only used if there is no matching foreign_proc version.
> > +% Note that this version only works if the Mercury implementation's
> > +% string representation allows strings to contain embedded null
> > +% characters.  So we check that.
> > +concat_string_list(StringsList, _Len, string_with_0s(StringWithNulls)) :-
> > +	(	
> > +		char__to_int(NullChar, 0),
> > +		NullCharString = string__char_to_string(NullChar),
> > +		string__length(NullCharString, 1)
> > +	->
> 
> I don't believe this test will succeed on any version of the current Mercury
> implementation.

It succeeds on the .NET back-end.  It should succeed on the Java
back-end too, once the relevant procedures such as string__length
are implemented for Java.

> The reason why I used C code to do the concatenation in the first place
> is that with a very few exceptions (such as string__index), the predicates
> in the string module all assume that strings are null terminated.
> String__length certainly does.

The C implementations of those predicates do.
But the .NET implementations don't.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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