Re: GIT version: values

[Hans Aberg <haberg-1@telia.com>]

On 27 Jan 2011, at 10:00, Andy Wingo wrote:

>>>   If you wish to preserve a potentially
>>>   multiply-valued return, you will need to set up a multiple-value
>>>   continuation, using `call-with-values'.
>>
>> But this is false.
>
> According to the standard, passing an unintended number of values to a
> continuation is undefined.

Right. Because of this, no extension is reliable - can be changed in  
the future.

> To portably preserve a potentially
> multiply-valued return, you need call-with-values.
>
> You can still implement other paradigms on top of this.  If you want  
> to
> express some semantics that is not specified in the report, write a
> macro that wraps your expressions in call-with-values.  This is
> effectively what we will do for Lua, for example.

Yes, this is what I do, first by a macro, and now, via a new tuple  
type (right now a smob), a function call.

But tuples might be integrated into Scheme, so that the underlying  
call-with-values become transparent.

For example, if (lambda x a) would have made the multiple values that  
x picks up as 'values', then (lambda x x) becomes the identity. Now  
this syntax is occupied, but it illustrates the idea.