[plt-scheme] struct introspection

Thank you. I read the part about using extract-struct-info inside a
macro, but didn't understand it until your example.

Todd

On Tue, May 25, 2010 at 5:48 PM, Jay McCarthy <jay.mccarthy at gmail.com> wrote:
> This program demonstrates some of your options:
>
> #lang racket
> (require (for-syntax racket/struct-info))
>
> (define-struct blah (a b c)
>  #:transparent)
>
> (define-syntax (static-get-fields stx)
>  (syntax-case stx ()
>    [(_ struct)
>     (let ([v (extract-struct-info (syntax-local-value #'struct))])
>       (quasisyntax/loc stx
>         (printf "~s\n" '#,v)))]))
>
> (define (dynamic-get-fields v)
>  (define-values (st skipped?) (struct-info v))
>  (define-values (name fields auto acc mut imm super sti-skipped?)
> (struct-type-info st))
>  (printf "~s\n" (list name fields)))
>
> (static-get-fields blah)
> (dynamic-get-fields (blah 1 2 3))
>
> It prints:
>
> (struct:blah make-blah blah? (blah-c blah-b blah-a) (#f #f #f) #t)
> (blah 3)
>
> As you can see, statically you can find out the names of the
> accessors, but dynamically you can only find out how many fields there
> are.
>
> Since someone can write:
>
> (define-struct funny-struct (funny-field) #:transparent)
>
> You can't reliably recover "field names" even though you can get the accessors.
>
> Jay
>
>
> On Tue, May 25, 2010 at 3:38 PM, Todd O'Bryan <toddobryan at gmail.com> wrote:
>> I feel like I've asked this before, but can't find it anywhere.
>>
>> If I
>>
>> (define-struct blah (a b c)
>>  #:transparent)
>>
>> is there any way to get the names of blah's fields?
>>
>> Todd
>> _________________________________________________
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>>
>
>
>
> --
> 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
>