Try Turtle: About Turtle Graphics Notation

Turtle Graphics notation is a turtle graphics language based upon Logo created for the book Turtle Geometry by Hal Abelson and Andrea diSessa.

This is not a complete implementation of that language and, in any case, I am unaware of any formal description of it. However, I like its old school charm, and made a simplified version of it. But you can learn how it works in the help.