[plt-scheme] Dot-notation for structure field access

From: jos koot (jos.koot at telefonica.net)
Date: Sun Mar 11 07:49:17 EDT 2007

Inspired by the dot notation of Jens Axel Søgaard I tried to eliminate the need for define-accessor. See enclosure. However, I can't get rid of the error reported at the end of my trial, reading:
"compile: bad syntax; reference to top-level identifier is not allowed, because no #%top syntax transformer is bound in: acc85"

Can anyone help me, please. Sorry that I don't send a stripped version of the problem. I have tried many stripped versions of my code, but in these the problem does not occur.

Greetings, Jos Koot

(((((lambda(x)((((((((x x)x)x)x)x)x)x)x))
    (lambda(x)(lambda(y)(x(x y)))))
  (lambda()(printf "Greetings, Jos~n"))))
  ----- Original Message ----- 
  From: Jens Axel Søgaard 
  To: George Herson 
  Cc: plt-scheme at list.cs.brown.edu 
  Sent: Thursday, March 08, 2007 11:13 PM
  Subject: [plt-scheme] Dot-notation for structure field access

  George Herson skrev:

  > May not be the best approach but I'm enjoying the
  > compactness of the resulting code (which allows
  > conventional table-name.column-name notation in a
  > sql-like mini-language).

  That remark sparked inspired me to play a little
  with #top in order to get the following to work:

  (require dot)
  (define-struct color (r g b) (make-inspector))

  (define-accessor r color-r)
  (define-accessor g color-g)
  (define-accessor b color-b)

  (define a (make-color 1 2 3))
  a.r  ; evaluates to 1
  a.g  ; evaluates to 2
  a.b  ; evaluates to 3

  The entire program, which by no means is well-tested, is below.

  /Jens Axel

  ; Put the entire program in a buffer, choose "Pretty Big"
  ; and click "Run".

  (module dot-helper mzscheme
     (provide dot define-accessor)

       (define accessors (list)))

     (require-for-syntax (prefix srfi: (lib "1.ss" "srfi")))
     (define-syntax (dot stx)
       (syntax-case stx ()
         [(dot expr accessor)
          #`(#,(cdr (srfi:assoc #'accessor accessors module-identifier=?))

     (define-syntax (define-accessor stx)
       (syntax-case stx ()
         [(define-accessor name getter)
            (set! accessors (cons (cons #'name #'getter)

  (module dot mzscheme
     (provide (rename my-top #%top)

     (require (lib "pregexp.ss")

     (define-for-syntax (contains-dot? sym)
       (member #\. (string->list
                    (symbol->string sym))))

     (define-for-syntax (split-at-dot sym)
         [(regexp-match #rx"^([^.]*)\\.([^.]*)$" (symbol->string sym))
          =>(lambda (result)
              (values (string->symbol (list-ref result 1))
                      (string->symbol (list-ref result 2))))]
         [else #f]))

     (define-syntax (my-top stx)
       (syntax-case stx ()
         [(_ . name)
          (and (identifier? #'name)
               (contains-dot? (syntax-e #'name)))
          (let-values ([(before after)
                        (split-at-dot (syntax-e #'name))])
            (with-syntax ([var (datum->syntax-object #'stx before)]
                          [acc (datum->syntax-object #'stx after)])
              #'(dot var acc)))]
         [(_ . name)
          #'(#%top . name)])))

  (require dot)
  (define-struct color (r g b) (make-inspector))

  (define-accessor r color-r)
  (define-accessor g color-g)
  (define-accessor b color-b)

  (define a (make-color 1 2 3))

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