s c h e m a t i c s : c o o k b o o k

> (define-struct s (a b) (make-inspector))
> (define x (make-s 1 2))
> x
#(struct:s 1 2)
> (s-a x)
1
> (s-b x)
2
> (require (lib "struct.ss"))
> (copy-struct s x [s-a 7])
#(struct:s 7 2)

(define-syntax (define-struct-update stx)
  (syntax-case stx ()
    [(_ struct update)
     (and (identifier? #'struct) (identifier? #'update))
     (with-syntax ([ellip '...])
       #'(define-syntax (update stx)
           (syntax-case stx ()
             [(_ s field-update ellip)
              (with-syntax ([(renamed-field-update ellip)
                             (map (lambda (field-update-stx)
                                    (syntax-case field-update-stx ()
                                      [(field v) (identifier? #'field)
                                                 (with-syntax ([renamed-field
                                                                (datum->syntax-object #'field
                                                                                      (string->symbol
                                                                                       (format "~a-~a"
                                                                                               'struct
                                                                                               (syntax-e #'field)))
                                                                                      #'field #'field #'field)])
                                                   #'(renamed-field v))]))
                                  (syntax->list #'(field-update ellip)))])
                #'(copy-struct struct s renamed-field-update ellip))])))]
    [(define-struct-update struct) #`(define-struct-update struct
                                       #,(datum->syntax-object stx 'update stx stx stx))]))

> (define-struct-update s)
> (update x [a 8])
#(struct:s 8 2)
> (define-struct-update s with)
> (with x [b 9])
#(struct:s 1 9)