[m-rev.] document Java foreign language interface

[Ralph Becket]

Fergus Henderson, Thursday,  4 December 2003:
> On 04-Dec-2003, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> 
> More seriously, I just realized that my original documentation was wrong:
> the success indicator goes at the start of the sequence, not at the end.

Putting it at the end did seem like an odd convention :-)

> How about this:
> 
>     The result of the Java function will be a sequence comprised of
>     the outputs of the Mercury procedure.  If the Mercury procedure's
>     determinism indicates that it can fail, then its first output will
>     be a @samp{boolean} success indicator, with a @samp{true} value
>     denoting success and a @samp{false} value denoting failure. The
>     remaining outputs will be the subsequence of the Mercury procedure's
>     arguments and function result (if any) that have output modes.

Sounds about right to me.  I don't think I'd have trouble understanding
that coming to it cold.

> > Hmmm... what's the mapping from data constructors to Java classes?  Or
> > is this private, in the sense that the programmer has to export field
> > accessor predicates to Java if they want to manipulate Mercury values
> > from within Java?
> 
> I'm happy to keep it private for now, and document it only in the source
> code (mlds.m, ml_type_gen.m and/or mlds_to_java.m) not in the language
> reference manual.  Currently the actual mapping is a bit too likely to
> change to document for users, IMHO.
> 
> Note that "pragma export" is not yet part of the language-independent
> foreign language interface chapter, and is not yet supported for Java.

Righto.

-- Ralph
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