Integrating Racket Classes and Struct Generics

gistfile1.rkt

#lang racket/base

(require racket/block
         racket/class
         racket/generic)

(define gar<%>
  (interface ()    
    do-foo
    do-bar))

(define-generics gar
  #:defaults
  ([(lambda (x) (is-a? x gar<%>))    
    (define gen-foo       (generic gar<%> do-foo))
    (define gen-bar       (generic gar<%> do-bar))
    (define (gar-foo x)   (send-generic x gen-foo))
    (define (gar-bar x y) (send-generic x gen-bar y))
    ])
  
  [gar-foo gar]
  [gar-bar gar y])

(define gar%
  (class* object% (gar<%>)    
    (define/public (do-foo)   'foo)
    (define/public (do-bar y) (list 'bar y))
    (super-new)))

(define bar%
  (class gar%
    (define/override (do-foo) 'foo2)
    (super-new)))