[racket] Void expression found

Here's what Jay is trying to say: 

Welcome to Racket v6.1.1.6.

This works: 

> (define (none) (values))
> (let-values ([() (none)]) 42)
42

This doesn't: 

> (let-values ([(x) (none)]) 21)
result arity mismatch;
 expected number of values not received
  expected: 1
  received: 0
  values...:
  context...:
   /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7

[No, return arity mismatch isn't a particularly explanatory error message.]

-- Matthias



On Jan 6, 2015, at 6:56 AM, Jay McCarthy wrote:

> They CAN return no values: (values)
> 
> It is just awkward because you get an error in the binding forms if you try to name the result (because there is none.)
> 
> Jay
> 
> On Monday, January 5, 2015, Jack Firth <jackhfirth at gmail.com> wrote:
> Given that racket has multiple return values, what sort of issues would arise if functions were allowed to return no values at all instead of opting to return the single value void when they have nothing to return? Is it purely a backwards compatibility thing, or are there more fundamental problems with that?
> 
> On Mon, Jan 5, 2015 at 4:46 PM, Hendrik Boom <hendrik at topoi.pooq.com> wrote:
> On Mon, Jan 05, 2015 at 05:58:31PM -0500, Sean Kanaley wrote:
> > I see "void" as a tangible value specifying no information, whereas
> > "undefined" is literally no information. So void is more like an empty
> > universe and undefined is no universe at all.
> 
> Algol 68 had a void value, called 'empty' in the defining report, but
> it didn't need a name in the language itself, because there were too
> many easy ways of geerating it.
> 
> I always considered void to be a type with exactly one value, which
> would need log2(1) bits to reprresent it, i.e., zero.
> 
> The report also left a number of things undefined.  An early draft of
> the report went on to specify 'undefined' as meaning anything from a
> reasonable continuation of the computation to 'indescribable chaos'.
> 
> -- hendrik
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
> 
> 
> 
> -- 
> Jay McCarthy
> http://jeapostrophe.github.io
> 
>            "Wherefore, be not weary in well-doing,
>       for ye are laying the foundation of a great work.
> And out of small things proceedeth that which is great."
>                           - D&C 64:33
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20150106/f6955a23/attachment-0001.html>