[racket] Contract for methods with optional arguments

Hi all:

	I have encountered a situation in which I don't know how to specify the 
contract for a method that:

1. Has a final optional argument
2. The value of the optional argument makes the method change the return 
type of the method.

It is similar to this:

(define/public (get-whatever (pos #f))
   (if (not pos)
       inner-vector-of-int
       (vector-ref inner-vector-of-int pos)))

(that is, if you don't specify a position, return the whole vector, but if 
you specify a position, return that position).

	For what I've seen in the documentation, there exists the ->i function 
that allos the specification of named parameters, such as (not working but 
you get the idea):

(->i () ;; mandatory
      ([pos (or/c number? boolean?)])  ;; optional
      [result (pos) (or/c (and/c (=/c #f pos) (vectorof number?))
                          (and/c (number? pos) number?))])

(I don't think the result expression is correct, but it expresses what I want).

	The real problem comes with methods, because I have ->m and ->dm, but not 
->im (->dm does not allow specifying dependent previous values in the 
result, for example, as far as I know).

	So the question is, how to write a method contract for this method?

	Thanks in advance,
	diego.

-- 
Diego Sevilla Ruiz -- http://ditec.um.es/~dsevilla/ -- dsevilla at um.es _.___
Dep. Ingeniería y Tecnología de Computadores, Facultad de Informática D|TEC
Univ.de Murcia,Campus Espinardo,30080 Murcia (SPAIN),Tel.+34868887571