[plt-scheme] Added section in my oop tutorial for inheritance and mixins; comments?

Danny Yoo wrote:

> Hi everyone,
>
> Sorry for being so late about this, but I restarted work on getting 
> that "class.ss tutorial for Java programmers" thing more fleshed out.  
> One of the requests I received was to add a section on mixins, so I 
> wrote something up that shows where they can be useful.  I also 
> fleshed out the section on inheritance a little more to explain to 
> myself some of the differences between inherit vs. send, just from an 
> early error-trapping perspective.
>
> Would anyone like to suggest improvements and corrections to this? 
> Here's a link to the revised tutorial:
>
>     http://hkn.eecs.berkeley.edu/~dyoo/plt/oop-notes.text

Its a nice tutorial, I wish I had something like this when I was 
starting to learn the class.ss module. About mixins why not use the 
given functionality of (mixin) of class.ss? I suppose its just a simple 
macro but why reinvent the wheel.
http://download.plt-scheme.org/doc/301/html/mzlib/mzlib-Z-H-4.html#node_sec_4.6


Also would you mind adding something on generic field accessors? I dont 
think it was completely obvious to me in the beginning why they were useful.