"void-valued expression where value is needed"

"void-valued expression where value is needed"

[Panicz Maciej Godek]

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Suppose that I have some code like

(define (f)::void
  (call-with-values
      (λ () #!void)
    (λ result
      (apply values result))))

When I compile it, Kawa issues the warning:

void-valued expression where value is needed

I wonder whether this warning is desired in such circumstances?

(It surely makes it difficult to write values-agnostic macros)

What is interesting is that the warning disappears if I replace #!void with
(values) [unless I declare the function's return type as ::void].

Re: "void-valued expression where value is needed"

[Arvydas Silanskas]

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I think this is a sensible warning. If I see #!void ending up somewhere
inside a value object like a list (`result` in your snippet), that
immediately alarms me that something is wrong. An empty `values` call is a
defined case, it would simply yield an empty `result` list.

2022-09-21, tr, 00:02 Panicz Maciej Godek via Kawa <kawa@sourceware.org>
rašė:

> Suppose that I have some code like
>
> (define (f)::void
>   (call-with-values
>       (λ () #!void)
>     (λ result
>       (apply values result))))
>
> When I compile it, Kawa issues the warning:
>
> void-valued expression where value is needed
>
> I wonder whether this warning is desired in such circumstances?
>
> (It surely makes it difficult to write values-agnostic macros)
>
> What is interesting is that the warning disappears if I replace #!void with
> (values) [unless I declare the function's return type as ::void].
>