Re: Questions about #!key arguments

[Taylor Venable <venablet at ipfw dot edu>]

On 10/25/2011 03:27 PM, Per Bothner wrote:
> We probably also want to re-think keyword arguments a bit. Given:
> (lambda (a1 a2 #!key k1 k2 #!rest r) ...)
> The existing "standard" is that r *includes* the keyword arguments.
> I'm not sure is this is what is most useful. For a typical "builder"
> function (HTML builder, Swing builder, etc) you want keyword arguments
> for named properties followed by "child" expressions. You don't want
> all the keyword bindings mixed up with the child parameters.
>
> So I think we need a new delimiter - I thought of #!tail. This is like
> #!rest, but it does *not* include any keyword arguments, and if there
> are keyword arguments not matched by keyword parameters, then it
> is an error.
>
> Does this make sense? Suggestions for a better name than #!tail?
> (Note that adding this may not happen soon.)

I haven't been using Kawa for very long, so I don't know much about its 
internals, but I humbly submit that there might be another option to 
implement #!rest like Gambit does. If #!rest appears before #!key then 
it contains the keywords; if #!rest appears after #!key then it does not.

Example below, full details at [1].

$ gsi
Gambit v4.6.2

> (define (foo-1 #!rest r #!key (a 2) (b 3)) (values (+ a b) r))
> (define (foo-2 #!key (a 2) (b 3) #!rest r) (values (+ a b) r))
> (foo-1 1 2 3 4)
5
(1 2 3 4)
> (foo-2 1 2 3 4)
5
(1 2 3 4)
> (foo-1 a: 0 b: 42 1 2 3 4)
42
(a: 0 b: 42 1 2 3 4)
> (foo-2 a: 0 b: 42 1 2 3 4)
42
(1 2 3 4)

[1] 
http://www.iro.umontreal.ca/~gambit/doc/gambit-c.html#Extensions-to-standard-special-forms