Hi Robert,

Robert Vollmert <rob@vllmrt.net> writes:

> Hi Timothy,
>
> thanks for the detailed feedback, this is very helpful!

You’re welcome!

> I’ve sent an updated patch addressing some of the concerns, but have
> some questions regarding others. (I just realized that the documentation
> updates probably anticipate multiple return values.)

Yes.

>> On 13. Jun 2019, at 04:28, Timothy Sample <samplet@ngyro.com> wrote:
>>> +  (let-values (((port get-hash) (open-sha256-input-port port)))
>
>>> +    (cons
>>> +      (read-cabal (canonical-newline-port port))
>>> +      (bytevector->nix-base32-string (get-hash)))))
>
> […]
>
>> Also, I think returning multiple values would be more natural here
>> (i.e., replace “cons” with “values”).
>
> I tried building it that way to begin with, but I’m having issues
> making it work (nicely, or maybe at all). I think it comes down to
> later functions optionally failing with a single #f-value. Judging
> by the lack of infrastructure, I imagine functions that return different
> numbers of values are not idiomatic scheme. Should this be changed to
> return two values (#f #f) on failure? Or to raise an exception and
> handle it higher up when we want to ignore a failure?
>
> Currently, implementing this with values/let-values results in me
> doing more or less a combination of let-values and match, at which
> point it seems that any potential benefits of using multiple values
> as opposed to a pair/list are lost. (There’s no match-values form is
> there?)

I’m not sure I understand the problem.  Here’s what I had in mind: