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Re: Can array-ref return (values ...) ?

This page is part of the web mail archives of SRFI 25 from before July 7th, 2015. The new archives for SRFI 25 contain all messages, not just those from before July 7th, 2015.

Brad Lucier <lucier@xxxxxxxxxxxxxxxx> writes:
> <David Rush topic="(values ...)">
> Ok, it's a procedure that accesses the current continuation
> then. It is a very odd procedure in since it can only be called in
> tail position. It *still* does not construct a data object, so it
> cannot be the "contents" of an array element.
> </ David Rush>
> we can use these procedures and macros to build new data
> abstractions if we want.
> So we could have (array-ref a i) and (array-set! a i v)
> be special forms (macros) that expand to
> (call-with-values
>     (lambda () i)
>   (lambda indices
>     (array-body-ref a indices)))
> and
> (call-with-values
>     (lambda () i)
>   (lambda indices
>     (call-with-values
> 	(lambda () v)
>       (lambda vals
> 	(array-body-set! a indices vals)))))

This just moves the problem down one layer. What do you get from it?
At some point you get to storage, which is what I originally
understood your reference to the "contents" of an array-ref to
be. There is still no way to store the 'result' from the VALUES form

If what you're getting at is that you want to specify array-ref and
array-set! as fully abstract operations with reference to a concrete
representation, this might have some more value. My concern with the
array abstraction issue has been that I have a top-level interface
that I can specialize easily (via macrology/modularity/functorization). 

Is this what we're arguing about? If it is, I think that the focus
should remain on the top-level interface. Implementations are free to
do what they want.

> So I don't believe these vehement denials that this is possible.

I think we're getting bogged down in what we're saying is
(im)possible. You can't store the 'result' of evaluating a VALUES
form. You certainly can use VALUES to implement a particular

david rush
C makes it easy to shoot yourself in the foot, C++ makes it harder,
but when you do, it blows away your whole leg -- Bjarne Stroustrup