[racket] a little macro exercise

Carl, yours doesn't pass the test suite.

For example, you return (void) rather than 3.

I've fixed that, removed the letrec and added else support.

http://github.com/jeapostrophe/exp/blob/master/cas-cad-e.rkt

Jay

On Sat, Oct 9, 2010 at 7:52 AM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> Here's my solution.  It is pure (if you ignore the set! nature of
> letrec), has linear expansion, avoids multiple values, and uses a
> single "case" for conditional tests.  The only thing it lacks that I
> know of is support for "else".
>
> --------------------------------------------------------------------------------
> #lang racket
> (require (for-syntax syntax/parse) racket/stxparam)
>
> (define-syntax-parameter break
>  (lambda (stx) (raise-syntax-error #f "used outside of cas-cad-e" stx)))
>
> (define-syntax cas-cad-e
>  (syntax-parser
>    [(_ e:expr [(v ...) body:expr ...+] ...)
>     (with-syntax ([(id ...) (generate-temporaries #'((v ...) ...))])
>       (with-syntax ([(f ...) #'(start id ... finish)]
>                     [(action ...) #'((begin) (begin body ...) ... (begin))]
>                     [(next ...) #'(id ... finish void)])
>         #'(let/ec escape
>             (syntax-parameterize ([break (make-rename-transformer #'escape)])
>               (letrec ([f (lambda () action (next))] ...)
>                 (case e [(v ...) (id)] ...))))))]))
>
> (define (nursery-rhyme n)
>  (cas-cad-e n
>    [(1 2) (displayln "buckle my shoe")]
>    [(3 4) (displayln "shut the door") (break)]
>    [(5 6) (displayln "pick up sticks")]
>    [(7 8) (displayln "lay them straight") (break)]
>    [(9 10) (displayln "a big fat hen")]))
>
> (for ([i '(1 2 3 4 5 6 7 8 9 10)])
>  (nursery-rhyme i))
> --------------------------------------------------------------------------------
>
> Carl Eastlund
>



-- 
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://teammccarthy.org/jay

"The glory of God is Intelligence" - D&C 93