how to pass a keyword as an argument?

[Sebastian Egner <sebastian.egner@philips.com>]

Maybe you have solved that already, but just for clarification:

If keywords are just constants (like integers), but
procedure application recognizes these keywords to
supply keyword-arguments, then how do I pass a keyword
value to a procedure? 

Is there any syntactic difference at the call site,
i.e. 
can I determine from (paint color: "red")
whether paint has
one (named color:) or two arguments (a keyword and
a string)?

As an alternative, the ambiguity would go away if
the
syntax extension requires parentheses for the keyword-
arguments. This might even allow simple implementations
as 'implicitly defined procedures', i.e. each identifier
ending in ':', say <keyword>:, is defined as


  (lambda args (apply make-option '<keyword>
args)),

where <keyword> is a lexical variable. The only
modification
to procedure calls is that they collect all the optional
arguments in a special variable available to the procedure.
It boils down to syntax like (paint (color: "red")
(button: 'push)).

[I am in favor of your mechanism for named arguments
but
would like to explore the implications and alternatives.]

Sebastian.