[Grace-core] First Grace lab in our intro course

[Kim Bruce]

We have just completed the first lab in our intro course using Grace.  We used Tim's editor/compiler installed at 
	http://www.cs.pomona.edu/~kim/minigrace/

The good news is that we had no problems with the Grace implementation (though there are some error checks that would be useful to add).  One student got stuck in Firefox hell (a ".parentlock" file buried deep in directories that kept him from running Firefox).  We eventually figured it out (I had it happen to me during lecture as well), and after that everything was fine.  Of course students had the usual logical errors of making multiple copies of the same geometric object in the same location and then not understanding why they wouldn't disappear or change color on command (one of the many stacked up did, but the others didn't).

The one puzzling error that could use better error messages is when students redefine the same identifier or method.  I had students think they had to repeat the "def name = " prefix every time they used the name, while others had two copies of onMousePress and then wondered why only the second was executed.  It would be helpful for those to be errors (for methods at least) or warnings (for defs).

Otherwise everything is going well.

Kim