cl-format: ~( thows an exception with an empty string

Answer: cl-format doesn't print nil as "Nil". The ₍) construction is a case control operator. In this case, it capitalizes the each word in the expression: http://www.lispworks.com/documentation/HyperSpec/Body/22_cha.htm.

In general, I've suppressed the obvious "CL-only" stuff like upper case symbols and such and replaced them with the corresponding Clojure conventions.

Patch works. One question: Why does cl-format print "nil" as "Nil"? Is this a CL-ism? Do we want it?

Patch that fixes the issue and adds tests

The following block of code throws an index out of range exception: