Did you make an interpreter in one lecture? Or did you just add a new macro to an existing language? S-expressions are tidy, tidy things, but just the underlying tech used to build a lexer, parser and interpreter takes a good while to understand, much less learn to write that quickly.<p>Lisper just reminded me of some HN commenter who once wrote that &quot;any idiot can build Youtube, it&#x27;s making it scale that&#x27;s hard&quot;, and that guy gets on my nerves. Sorry about projecting that onto lisper.