What is the data structure behind Clojure's sets?

Question

I recently listened to Rich Hickey\'s interview on Software Engineering Radio. During the interview Rich mentioned that Clojure\'s collections are implemented as trees. I\'m

Answer 1

You should really read Clojure Programming, it covers this in great detail, including pictures. Briefly though, collections are depth first searches through trees. We can show your examples like this:

(def x #{1 2 3})

x
|
| \
|\ 3
1 \
   2

(def y (conj x 4))

 x  y
 | / \
 | \   4
 |\ 3
 1 \
    2

 (def z (difference y #{1}))

 x  y
 | / \
 | \  4
 |\ 3
 1/\
z-  2

Note that these are just indicative, I'm not saying that this is exactly the layout Clojure uses internally. It's the gist though.