There's not much power here, Streem doesn't even have a semantics yet so I don't know what this repository is implementing. They just picked something easy to write and slapped the Streem label on it and oh yeah, Lisp!!
Just to make it clear, the author discloses that beyond the sample it doesn't work, and there's lots of problems he doesn't tackle.
Also, from the tone of it, one should have no expectation of this going further. It seems mostly aimed to be a test of how it would look like in lisp and nothing more.