[racket] Problem with macro

2011/8/11 Racket Noob <racketnoob at hotmail.com>:
> Hi all!
>
> I want to create macro for creating a DFA automaton (similar to
> one described
> here: http://www.cs.brown.edu/~sk/Publications/Papers/Published/sk-automata-macros/paper.pdf )
>
> My desire is that, for example, this form
>
> (automaton init
>    (init : (c -> more))
>    (more : (a -> more)
>            (d -> more)
>            (r -> END)))
>
> expands to:
>
> (letrec ([curr-state empty]
>            [init
>             (lambda (symbol)
>               (case symbol
>                 [(c) (set! curr-state more) 'ok]
>                 [else 'transition-error]))]
>            [more
>             (lambda (symbol)
>               (case symbol
>                 [(a) (set! curr-state more) 'ok]
>                 [(d) (set! curr-state more) 'ok]
>                 [(r) (set! curr-state END) 'endstate]
>                 [else 'transition-error]))]
>            [END
>             (lambda (symbol)
>               'reading-past-end-error)])
>     (set! curr-state init)
>     (lambda (c)
>       (curr-state c))))
>
>
> I've created the following two macros, but unfortunatelly they are wrong:
>
> (define-syntax process-state
>   (syntax-rules (: -> END)
>     [(_ (label -> END))
>      [(label) (set! curr-state END) 'endstate]]
>     [(_ (label -> new-state))
>      [(label) (set! curr-state new-state) 'ok]]))
>
>
> (define-syntax automaton
>   (syntax-rules (: -> END)
>     [(_ init-state
>         (state : transition ...)
>         ...)
>      (letrec ([curr-state empty]
>               [state
>                (lambda (symbol)
>                  (case symbol
>                    [(process-state transition)]

The line above here should be a case clause, but it only has one part.
I think you meant [process-state transition]

Jay

>                    ...
>                    [else 'transition-error]))]
>               ...
>               [END
>                (lambda (symbol)
>                  'reading-past-end-error)])
>        (set! curr-state init-state)
>        (lambda (c)
>          (curr-state c)))]))
>
> Reported error is: case: bad syntax (missing expression after datum
> sequence) in: ((process-state (c -> more)))
> It seems to me that macro process-state is not expanding at all.
>
> Can somebody tell me what's wrong and how to fix it???
>
> Thanks in advance,
> Racket Noob
>
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-- 
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://faculty.cs.byu.edu/~jay

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