Why would you write a Lisp interpreter?
I find that question difficult to answer, but the joy of open source is that I don’t have to answer it.
Subs is very incomplete, and will probably never be otherwise, but it is exciting how quickly you can write a functional Lisp interpreter. I plan to go through SICP section by section and ensure all the examples work in Subs. So far I am failing on the last example in section 1.1.1 (because I don’t support new-lines inside statements yet!) but in reality most of the work is done to support quite a lot of stuff (NOT including mutable variables…yuck).
One possible explanation, if such a thing were necessary, is that one day I want to write a new programming language that has all the simplicity and metaprogramming capability of Lisp, with the native performance and deployability of C++, and the syntactic elegance of Python. I’ve got a lot to learn first.