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>... 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))
--lars