[plt-scheme] keyword arguments, take 2

On Jun 14, Carl Eastlund wrote:
> I like the proposal for a lot of reasons.  One thing discussed
> around the office here at NU that it doesn't address is keywords
> with more/less than one argument.  For instance, keywords can
> conceptually be used alone (i.e. as flags, as in (open "/dev/random"
> #:read-only)), or have multiple arguments (Ryan's example was
> (connect #:tcp "localhost" 80) -- connect takes a keyword specifying
> a protocol, and the keyword takes however many arguments the
> protocol needs).  I don't have an immediate counterproposal for how
> to include these, but I think they can be useful features,
> especially the zero-argument "flag" use.

Some quick comments about this:

1. The `#:read-only' example is not a good one.  That's a case where
   it would have been better to use a `mode' argument with a symbol
   value.

2. I'm not sure that `flag' arguments (in the sense of the current
   "kw.ss") are useful.  They were hacked on by Sam's request, but
   never really used by him.  I don't know of any other uses of these
   flags, so I think that that it wouldn't be a problem to give up
   that feature.

3. Finally, for the multi-values bound to different names, you can
   want the same without keywords:
     (define (connect mode (host port)) ...)
     (connect 'tcp ("localhost" 80))

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