[m-dev.] export declarations

[Peter Schachte]

On Fri, 21 Nov 1997, Fergus Henderson wrote:
> Peter Schachte, you wrote:
> > I think the pragma should really be 
> > 
> > 	:- pragma c_export(Pred(Mode1, Mode2, ...), "C_Name_1").
> > 
> > and similarly for functions.  Alternatively, it could be something like:
> > 
> > 	:- pragma export(Pred(Mode1, Mode2, ...), c("C_Name_1")).
> 
> I was thinking of an extra argument, i.e.
> 
>  	:- pragma export(Pred(Mode1, Mode2, ...), 'C', "C_Name_1").
>  	:- pragma export(Pred(Mode1, Mode2, ...), 'Prolog', "Prolog_Name_1").
>  	:- pragma export(Pred(Mode1, Mode2, ...), 'Ada', "Ada_Name_1").
>  	:- pragma export(Pred(Mode1, Mode2, ...), 'Java', "Java_Name_1").

The trouble with that is it doesn't give you the opportunity to specify
different information for different languages.  For example, for an
assembler interface you might want to specify a list of register names to
pass parameters in, or who knows what information you might want for C++ to
be able to write a method directly in Mercury.  You might also like the
option of having the name just default to the predicate name, so you could
allow all of:

	:- pragma export(foo(...), c("Foo")).
	:- pragma export(bar(...), c).
	:- pragma export(baz(...), asm([r1,r3,r2,r2])).

Each implementation would decide which sorts of export terms to support.

> Another feature which may be useful: the Ada `pragma export' (which
> was a major source of inspiration for the Mercury `pragma export')
> allows you to specify the assembler-level link name instead of the
> external language name.

This could be handled with something like

	:- pragma export(foo(...), c_with_asm_name("@foo")).

or maybe

	:- pragma export(foo(...), c("@foo",[asm_name])).

(the second argument being a list of options), or possibly

	:- pragma export(foo(...), c(asm_name("@foo"))).

(the idea being that the name can be wrapped with asm_name/1 for any
language; nice orthogonality, but not as pretty).

Either of the approaches I initially suggested gives you a flexible
framework into which you can put all kinds of things later, which simply
adding a language name argument doesn't.


-Peter Schachte			| Politicians are the same all over. They
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