Re: [Chicken-users] multiple values in chicken

[Tobia Conforto]

From the other thread

Elf wrote:
> John Cowan wrote:
> > It also occurs to me that rec and let-values and all need not  
> > expand into call-values--that's just the *portable* expansion of  
> > them.
>
> they'll all be call-with-values on the inside, or the equivalent  
> thereof.

Not necessarily.

I see what John is proposing here, and it makes sense to me.

We could choose values and receive (or let-values) to be the primitive  
calls and relegate call-with-values to the role of a somewhat  
inefficient wrapper, included for the sake of conformance.

- (values 1 2) could put the two values in registers or stack  
locations, without unnecessary consing, taking care to put the first  
returned value in the conventional register for single return values;
- (receive (x y) ...) and the equivalent let-values form would just  
give names to those conventional registers or stack locations, without  
any destructuring;
- other consuming forms could just use the first returned value and  
ignore the others, as they currently do;
- (call-with-values) would be a bit more complex, because it would  
need to emulate all the calling and consing semantics, but I'd wager  
it's doable.

Sorry if I can't be more precise (and clever), but I don't know  
Chicken's internals very well (yet)

Making multiple return values as optimized as a single C call seems  
doable and very useful to me, even if it means optimizing for  
(receive) and (let-values) on the receiving side, instead of (call- 
with-values).

What do you think?


Tobia