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

[jos koot]

Skipped content of type multipart/alternative-------------- next part --------------
; Language: Textual (MzScheme, includes R5RS), DrScheme version 369.8-svn9mar2007 [3m].

(module dot mzscheme ; for dotted notation of struct-fields for both references and assignments.
  
 (define-for-syntax (compare-id? a b)
  (or
   (module-identifier=? a b)
   (free-identifier=?   a b)
   (bound-identifier=?  a b)))
 
 (define-for-syntax register ())
 
 (define-for-syntax (register-add! constr proc) (set! register (cons (cons constr proc) register)))
 
 (define-for-syntax (register-lookup constr)
  (let register-lookup ((register register))
   (cond
    ((null? register) (raise-syntax-error 'module-dot "unknown struct-constructor" constr constr))
    ((compare-id? (caar register) constr) (cdar register))
    (else (register-lookup (cdr register))))))
 
 (define-for-syntax (make-id var field)
  (datum->syntax-object var (string->symbol (string-append (symbol->string (syntax-e var)) "." (symbol->string (syntax-e field))))))
 
 (define-for-syntax (register-transformer-builder constr fields acc mut)
  (register-add! constr
   (lambda (var)
    (let ((n 0))
     (map
      (lambda (field)
       (let ((dotted-var (make-id var field)))
        (begin0
       #`(define-syntax #,dotted-var
          (make-set!-transformer
           (lambda (stx) 
            (syntax-case stx (set!)
             ((set! id v) #'((make-struct-field-mutator #,mut #,n) #,var v))
             ((id x (... ...)) #'(((make-struct-field-accessor #,acc #,n) #,var) x (... ...)))
             (id #'((make-struct-field-accessor #,acc #,n) #,var))))))
         (set! n (add1 n)))))
      (syntax->list fields))))))
 
 (define-syntax (define-struct-type stx)
  (syntax-case stx ()
   ((define-struct-type  descr constr pred        (field ...)          )
  #'(define-struct-type (descr constr pred #f   ) (field ...) #f       ))
   ((define-struct-type  descr constr pred        (field ...) inspector)
  #'(define-struct-type (descr constr pred #f   ) (field ...) inspector))
   ((define-struct-type (descr constr pred      ) (field ...)          )
  #'(define-struct-type (descr constr pred #f   ) (field ...) #f       ))
   ((define-struct-type (descr constr pred super) (field ...)          )
  #'(define-struct-type (descr constr pred super) (field ...) #f       ))
   ((define-struct-type (descr constr pred      ) (field ...) inspector)
  #'(define-struct-type (descr constr pred #f   ) (field ...) inspector))
   ((define-struct-type (descr constr pred super) (field ...) inspector)
    (let-values (((acc mut) (apply values (generate-temporaries #'(acc mut)))))
     (register-transformer-builder #'constr #'(field ...) acc mut)
   #`(define-values (descr constr pred #,acc #,mut)
      (let-values
       (((descr constr pred #,acc #,mut)
         (make-struct-type 'descr super #,(length (syntax->list #'(field ...))) 0 #f () inspector #f () #f)))
       (values descr constr pred #,acc #,mut)))))))
 
 (define-syntax (define-struct-var stx)
  (syntax-case stx ()
   ((define-struct-var var (constr expr ...))
  #`(begin
     (define var (constr expr ...))
  #,@((register-lookup #'constr) #'var)))))
 
 (define-syntax let-struct-type
  (syntax-rules ()
   ((let-struct-type (binding ...) . rest)
    (let () (define-struct-type . binding) ... . rest))))
 
 (define-syntax let-struct-var
  (syntax-rules ()
   ((let-struct-var (binding ...) . rest)
    (let () (define-struct-var . binding) ... . rest))))
 
 (provide define-struct-type define-struct-var let-struct-type let-struct-var))

(require dot)

"one"                                               ; --> "one"
(define-struct-type d c p (x y z) (make-inspector))
"two"                                               ; --> "two"
(define-struct-var s (c 1 2 add1))
"three"                                             ; --> "three"
d                                                   ; --> #<struct-type:d>
c                                                   ; --> #<primitive:make-d>
p                                                   ; --> #<primitive:d?>
s                                                   ; --> #(struct:d 1 2 3)
(p s)
"four"                                              ; --> "four"
s.x          ; error : compile: bad syntax; reference to top-level identifier is not allowed, because no #%top syntax transformer is bound in: acc1
(set! s.x 3) ; error : compile: bad syntax; reference to top-level identifier is not allowed, because no #%top syntax transformer is bound in: mut2