[racket] happy april fools day: arctangent 0.1

Arctangent is more practical than the DrBASIC that I started but didn't 
get back to in time for April 1st.  (Line numbers, and everything.  And 
who of us who were tots in the '80s realized that "NEXT A" wasn't 
necessarily lexical.) :)

Incidentally, defining new languages in Racket nowadays is a bit more 
pleasant than it was in PLT Scheme 3xx only a few years ago.  I spent a 
couple weekends implementing Arc in PLT before it stopped being fun.  
http://www.neilvandyke.org/morc/

If anyone is inspired by Danny's recent languages to implement another 
"#lang" for Racket, the SICP language could use reimplementing in a more 
clean way.  http://www.neilvandyke.org/racket-sicp/

BTW, Arc does seem like a pretty good example to use in a tutorial, 
since you can mostly use the normal Racket reader, yet the language 
looks different enough, and the implementation is nontrivial.  Chapter 2 
of the tutorial uses the example of translating Python? :)

Neil V.

-- 
http://www.neilvandyke.org/