[m-dev.] Re: Documentation of support for polymorphic pragma c code

[Peter Schachte]

On Wed, 14 Jan 1998, Oliver Hutchison wrote:

> :- pred fug(T1, T2).
> :- mode fug(in, out) is det.
> 
> fug(A, B) :-
> 	TypeInfo_for_T1 = type_of(A),
> 	TypeInfo_for_T2 = type_of(B),
> 	fug2(TypeInfo_for_T1, TypeInfo_for_T2, A, B).
> 
> :- pred fug2(type_info, type_info, T1, T2).
> :- mode fug2(in, in, in, out).
> 
> :- pragma c_code(fug2(TypeInfo_for_T1::in, TypeInfo_for_T2::in, A::in,
> 		B::in), "
> 	do_some_stuff(TypeInfo_for_T1, TypeInfo_for_T2, A, B);
> ").
> 
> 
> could be written 
> 
> :- pred fug(T1, T2).
> :- mode fug(in, out) is det.
> 
> :- pragma c_code(fug(A::in, B::in) ,"
> 	do_some_stuff(TypeInfo_for_T1, TypeInfo_for_T2, A, B);
> ").
> 
> 
> I know I like the second alternative.

The (well, one) trouble with documenting this is that it puts the way type
infos are handled into the language.  I really don't think it belongs there. 

I guess the following would be quite horrible to try to implement, but I'd
really like to write something like this: 

:- pred fug(T1, T2).
:- mode fug(in, out) is det.

:- pragma c_code(fug(A::in, B::in) ,"
	do_some_stuff(MR_TYPE_INFO(T1,1), MR_TYPE_INFO(T2,1), A, B);
").

(The second argument to MR_TYPE_INFO being the parameter number of the type
of the first argument, needed for multiparametric types).


-Peter Schachte			| The wrong sort of people are always in power
pets at cs.mu.OZ.AU		| because they would not be in power if they
http://www.cs.mu.oz.au/~pets/	| were not the wrong sort of people. -- Jon
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