[racket] Call by reference macro example in Racket Guide

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On 14-12-11 21:19, Harry Spier wrote:
> Dear list members,
> 
> In the Racket Guide 16.1.7 Extended Example: Call-by-Reference 
> Functions it shows how with macros to set up call by reference 
> versions of Racket functions.
> 
> I'm a little bit confused on why for the example, the macro (swap
> x y) was used as the example function to turn into a 
> call-by-reference function, since doesn't the macro (swap x y) 
> already act like a call-by-reference function.

I think the point is to contrast

  (define (f x y) (swap x y))

with

  (define-cbr (f x y) (swap x y)).

That first f is a function that swaps its local arguments with no
change to the outside world, while the second f is a macro (IIUC) that
mutates its real (for lack of a better term (on my part)) arguments,
through the macro magic of define-cbr.

Marijn
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