There are far too many implementations of Scheme out there, and probably too many of Common Lisp. However, that is beside the point that we did not come to praise the existing dialects of Lisp, by implementing them again.

Spark will be a completely different dialect of Lisp. It won’t be compatible with either Scheme (or any of its implementations), Common Lisp or even with Arc. It will still be Lisp, though, as we hope you will see.