At 5:37 PM -0500 1/20/00, Lars Thomas Hansen wrote:
>  >... but I fail to see the appeal of this mechanism. As far as I can
>  >tell, a scheme implementation which conforms to this SRFI allows me
>  >to write
>  >
>  >(set! (car x) 5)
>  >
>  >rather than
>  >
>  >(set-car! x 5)
>
>It's useful for syntactic (rather than procedural) abstraction.  It
>allows you to write macros like this:
>
>   ;; inc! increments whatever is stored in the "location" that
>   ;; is its argument.
>
>   (define-syntax inc!
>     (syntax-rules ()
>       ((inc! ?loc)
>        (set! ?loc (+ ?loc 1)))))
>
>Without SRFI-17, you can at most pass a variable as a location:
>
>   (inc! x)  => (set! x (+ x 1))
>
>but with SRFI-17 you can do better:
>
>   (inc! (car x)) => (set! (car x) (+ (car x) 1))
>   (inc! (vector-ref v i)) => (set! (vector-ref v i) (+ (vector-ref v i) 1))
>

Let me clarify.  I have nothing against syntactic abstraction.  My
concern is primarily with the unnecessary overloading of the set!
primitive.  Replace set! with set-location! (or set-l! if you prefer)
and you have a language extension which
a) I would not personally use, but
b) I would not object to (much).

john clements