Hello, Most of the GUI is defined in the directories starting at <racket installation directory>/collects/mred. I'm not sure what kind of extensions you're looking at doing, but the frame% class is defined in collects/mred/private/mrtop.rkt. And you would extend (sub-class) this and the other GUI classes in the normal way, e.g. (define my-frame% (class frame% (init [my-init-field <some default value>]) ; other definitions etc (super-new) (define/public (new-method x y z) ; my-method implementation ) (define/override (old-method x y z) ; override implementation ) ; other definitions etc. )) (define f (new my-frame% [my-init-field <some value>] ... )) (send f show #t) Hope this helps, Kieron. <div class="gmail_quote">On Fri, Sep 28, 2012 at 8:46 AM, <<a href="mailto:heraklea@gmx.de" target="_blank">heraklea@gmx.de</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello, where can I find the source to the gui modul. I would like to see how the gui framework is implemented. Is it possible to extend it with custom frames? Yours, ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </blockquote></div>