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

[Peter Schachte]

On Wed, 14 Jan 1998, Fergus Henderson wrote:

> > :- 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);
> > ").
> 
> That could be implemented very easily:
> 
> 	#define paste(x,y) x##y
> 	#define MR_TYPE_INFO(var) paste(TypeInfo_for_,var)

Cute....

> Using a macro like this puts a small layer of abstraction over
> the arguably ugly technique of using special variable names.
> On the other hand, I'm not sure it really adds much.

I just find it syntactically a bit cleaner.

> One potential drawback with this is that MR_TYPE_INFO() could only
> be used within the `pragma c_code'

True.

> > (The second argument to MR_TYPE_INFO being the parameter number of the type
> > of the first argument, needed for multiparametric types).
> 
> I don't understand why this is needed.

Nevermind.  I was just confused.


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