As the author of sibilant: A) it was/is fun B) I don't want to be dependent on another language — sibilant is entirely self-hosting, like coffeescript. Additionally, I don't want to be constrained to pure lisp. I'd like for sibilant to evolve into a language that incorporates the best elements of lisp and javascript. Since sibilant is written in sibilant, there's no dependence on pure lisp and the language can evolve in its own direction.

There's something satisfyingly elegant about using an interpreted language to interpret another language - macros can actually modify the compiler at compile-time, from within the language. I hope to make more use of this possibility in the future, as it's currently only used for macros.

Some reasons I can think of: it's definitely an advantage to be able to compile the code on the client-side, which sibilant should be able to do; I don't know if Parenscript can bootstrap itself the same way. Some people, like me, prefer lisp-1 to lisp-2. Being less like Common Lisp and more like Javascript can be an advantage; sibilant seems to support foo.bar notation for accessing JS properties, which I think is the right choice in this context (I would also like to see JS/JSON literal syntax supported).

All of the docs on Parenscript seem to assume you're using it to render bits of JS and HTML from a Common Lisp server. It would be useful if there were a tutorial that showed how to use Parenscript for this use case, simply to compile lisp-like code into standalone JS files for use with whatever arbitrary backend.

I don't know this particular author's intentions, but I can definitely see a reason to create a new Lisp over Javascript: I like functional programming, so I'd like something Schemey or Clojurey rather than CLish.