I "erase" the turtle be redrawing
it with the same color as the background but that does not look good as it
also erases everything ese. I tought of using large matrix (e.g 1000x1000) as
a representation of the turtle world and displaying it with contour() but it is slow
to update after each user command.
R's graphics aren't really designed for moving graphics, or undrawing things.
Perhaps you can use the tcltk library, you could draw on a tk canvas. This would be much more suited to turtle graphics.
If you want to get the turtle track back into R once the turtle has finished its wanderings then you can probably read the path from the Tk canvas widget into R using the tcltk library.
Or you may want to use python, instead of R: http://www.python.org/doc/current/lib/module-turtle.html
Or you may want to use Perl instead or R: http://home.hccnet.nl/kees.moerman/turtle.html
Both these systems use Tk as their graphics output.
I wrote some turtle-graphics subroutines for the ZX Spectrum about 20 years ago :)
Baz
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