Support "rest" arguments at the command line

[countvajhula]

Ordinary Racket functions accept individually named arguments, but also packed "rest" arguments using the dot notation:

(define (func . args)
   body ...)

With #lang cli, we'd like to support something similar:

(program (prog . args)
   body ...)

and

(program (prog . [args "Files to process"])
   body ...)

... would be ideal. But I seem to recall that it's tricky (impossible?) to match the literal dot in macros. So it may be necessary to use a custom syntax to indicate that arguments should be collected into a list. Example:

(program (prog (rest args))
   body ...)

and

(program (prog . (rest [args "Files to process"]))
   body ...)

Note that Racket's built-in command-line does support this kind of argument packing, and it too is implemented on top of parse-command-line, as #lang cli is. So it should be possible to leverage the built-in facilities for this.

Workaround: At the moment, we can use the multi constraint to pass multiple arguments via a flag.