On Tuesday, December 30, 2003 5:04 PM, Kevin S. Millikin [SMTP:kmillikin@atcorp.com] wrote:
Oh, sure. I didn't mean to quibble with the idea that continuations are computational effects. Just wanted to point out that (I think) you can't macro express mutation with call/cc, unless you've already got mutation anyway.
[snip]
Yup. If you do that, you can use d as your setter and c as your getter:
(define c (make-cell)) (define d c) ((d 'set) 9) (c 'get) 9 ((d 'set) 17) (c 'get) 17
It sure looks like the example contradicts the assertion, but I happen to know that there is a set! (or some other assignment) in the macro expansion of define. I'm just using call/cc to get at that, rather than getting at the one in the expansion of letrec. Moved to Haskell Cafe.