That is a lot more brief than mine. I just adapted a naive, unquoted
version from the Racket case:
(define-syntax my-case
(syntax-rules (else)
[(_ val ((mtch ...) expr) rest ... (else expr2))
(if (my-comp val (mtch ...))
expr
(my-case val rest ... (else expr2)))]
[(_ val ((mtch ...) expr) (else expr2))
(if (my-comp val (mtch ...))
expr
expr2)]
[(_ val (else expr)) expr]
[(_ val ((mtch ...) expr) rest ...)
(my-case val ((mtch ...) expr) rest ... (else #f))]))
(define-syntax my-comp
(syntax-rules ()
[(_ v ()) #f]
[(_ v (k)) (equal? v k)]
[(_ v (k ks ...)) (if (equal? v k)
#t
(my-comp v (ks ...)))]))
On Tue, Dec 23, 2014 at 8:29 PM, Eli Barzilay <e...@barzilay.org> wrote:
> On Mon, Dec 22, 2014 at 12:52 AM, Jon Zeppieri <zeppi...@gmail.com> wrote:
> > `case` is like C's `switch` (but unlike similar constructs in other
> > C's switch does, however, allow the use of constant *expressions* as
> > case labels, so you can have something like `case FOO % 3`, where `FOO
> > % 3` can be computed at compile-time.
>
> (define-syntax (case* stx)
> (syntax-case stx ()
> [(_ what [v e ...] ...)
> (with-syntax ([(v* ...) (generate-temporaries #'(v ...))])
> #'(let-syntax ([foo (λ(_) (with-syntax ([(v* ...) (list v ...)])
> #'(case what [(v*) e ...] ...)))])
> foo))]))
>
> (case* 3
> [1 2]
> [(+ 1 2) 4])
>
> --
> ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
> http://barzilay.org/ Maze is Life!
>
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