Growing a DSL - use longs and variable fixes

Hey, 

I came across the Growing a DSL with Clojure tutorial and it was fantastic, learnt quite a bit from it, especially being new to Clojure. 

Only noticed that some of the code wouldn't run in the REPL because of variables being wrong and switching based on Integer's didn't work. I'm guessing earlier versions of Clojure did, then they changed to Long's - not sure.

Cheers.