PHP/GD Cartesian equation plotter

http://www.therobert.org/stuff/tools/grapher/

Found this little tool lying on my server from a few years back when I decided to learn GD one night (and was still hooked on PHP). I needed some graphs and figured I'd make myself a right-click-save-as tool. The funnest part was writing the DSL mathematical expression parser. Try, for example:

   sincosx^2
   -tanlogx^e^x+-1x
   sin1/x^sqrt4

I wanted to implement multiple graphs, polar, and maybe 3D, but it was 1AM I think...Anyone done something similar?