It's written in Arc. Regarding the square bracket syntax: [... _ ...] is an abbreviation for (fn (_) (... _ ...)) http://www.paulgraham.com/arc.html htt

It's written in Arc. Regarding the square bracket syntax: [... _ ...] is an abbreviation for (fn (_) (... _ ...)) http://www.paulgraham.com/arc.html http://www.paulgraham.com/arc.html http://en.wikipedia.org/wiki/Arc_%28programming_language%29 http://en.wikipedia.org/wiki/Arc_%28programming_language%29