<html> <head> <meta content="text/html; charset=KOI8-R" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> Here is the code. I had to split the abstract methods from the concrete methods in the interface. The trick with mixins is that they can't be instantiated themselves, you have to apply them to some class and then instantiate that class. #lang racket (provide š first-child-class% š second-child-class%) (define child-interface-partial š (interface () šššššššššššš child-method šššššššššššš )) (define child-interface š (interface (child-interface-partial) šššššššššššš child-implementation-dependent-method)) #; (define generic-parent-class% š (class* object% () ššššššššš (super-new) ššššššššš (define/public (child-method this-time) (error 'child-method "abstract method")) ššššššššš (define/public (child-implementation-dependent-method given-inputs-list) ššššššššššš (map ššššššššššššš (lambda(this-item) ššššššššššššššš (eprintf "Next list item is ~v" (child-method this-item))) ššššššššššššš given-inputs-list)))) (define generic-parent-class-mixin š (mixin (child-interface-partial) šššššššš (child-interface) šššššššš (define/public (child-implementation-dependent-method given-inputs-list) ššššššššššš (map ššššššššššššš (lambda(this-item) ššššššššššššššš (eprintf "Next list item is ~v\n" (send this child-method this-item))) ššššššššššššš given-inputs-list)) šššššššš (super-new))) (define first-child-class% š (generic-parent-class-mixin ššššš (class* object% (child-interface-partial) ššššššššššššš (super-new) ššššššššššššš (define/public (child-method given-input) ššššššššššššššš (string-append "First gotš " given-input))))) (define second-child-class% š (generic-parent-class-mixin ššš (class* object% (child-interface-partial) ššššššššššš (super-new) ššššššššššš (define/public (child-method given-input) ššššššššššššš (string-append "Second gotš " given-input))))) (define x1 (new first-child-class%)) (define x2 (new second-child-class%)) (send x1 child-implementation-dependent-method '("a" "b" "c")) (send x2 child-implementation-dependent-method '("a" "b" "c")) Output: Next list item is "First gotš a" Next list item is "First gotš b" Next list item is "First gotš c" '(#<void> #<void> #<void>) Next list item is "Second gotš a" Next list item is "Second gotš b" Next list item is "Second gotš c" '(#<void> #<void> #<void>) On 08/24/2011 11:18 AM, Alexander Kasiukov wrote: <blockquote cite="mid:4E553267.1080100@sunysuffolk.edu" type="cite"> <meta http-equiv="content-type" content="text/html; charset=KOI8-R"> Dear Jon, Thank you very much for your help! I got what I needed to work with method overrides (following a suggestion of Robby Findler), but it does look like mixins may give a less redundant way to accomplish the same functionality. I am at a loss trying to understand how to make them work based on the Bakus-Naur description. (I am just starting to learn Racket and Lisp in general.) Could you show an example or suggest a place where I can look up one? I am trying to do something along the lines of #lang racket (provide ššš first-child-class% ššš second-child-class%) (define child-interface ššš (interface () ššš ššš child-implementation-dependent-method ššš ššš child-method)) (define generic-parent-class% ššš (class* object% () ššš ššš (super-new) ššš ššš (define/public (child-method this-time) (error 'child-method "abstract method")) ššš ššš (define/public (child-implementation-dependent-method given-inputs-list) ššš ššš ššš (map ššš ššš ššš ššš (lambda(this-item) ššš ššš ššš ššš ššš (eprintf "Next list item is ~v" (child-method this-item))) ššš ššš ššš ššš given-inputs-list)))) (define first-child-class% ššš (class* generic-parent-class% (child-interface) ššš ššš (super-new) ššš ššš (define/override (child-method given-input) ššš ššš ššš (string-append "First gotš " given-input)))) (define second-child-class% ššš (class* generic-parent-class% (child-interface) ššš ššš (super-new) ššš (define/override (child-method given-input) ššš ššš (string-append "Second gotš " given-input)))) Sincerely yours, Alex <blockquote type="cite"> <pre wrap="">Date: Wed, 24 Aug 2011 09:04:40 -0600 From: Jon Rafkind <a moz-do-not-send="true" class="moz-txt-link-rfc2396E" href="mailto:rafkind@cs.utah.edu"><rafkind@cs.utah.edu></a> To: <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:users@racket-lang.org">users@racket-lang.org</a> Subject: Re: [racket] How to use abstract classes? Message-ID: <a moz-do-not-send="true" class="moz-txt-link-rfc2396E" href="mailto:4E551308.5020503@cs.utah.edu"><4E551308.5020503@cs.utah.edu></a> Content-Type: text/plain; charset=ISO-8859-1 You could use a mixin. <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://docs.racket-lang.org/reference/mixins.html?q=mixin&q=class#%28form._%28%28lib._racket/private/class-internal..rkt%29._mixin%29%29">http://docs.racket-lang.org/reference/mixins.html?q=mixin&q=class#(form._((lib._racket/private/class-internal..rkt)._mixin))</a> On 08/24/2011 08:31 AM, Alexander Kasiukov wrote: </pre> <blockquote type="cite" style="color: #000000;"> <pre wrap="">Dear Racket users, What is the best way to make a class in Racket abstract? I would like to have a class which never gets instantiated implements certain methods common to all of its children needs to call some of the methods implemented in the children. Sincerely yours, Alex</pre> </blockquote> </blockquote> </blockquote> </body> </html>