Tuning tries (IntSet, hashmap, bytestring-trie, etc.)

[Jim Apple]

Given the recent faster trie implementations (hooray!), I thought it
would be worth pointing out that a pretty thorough discussion of the
tradeoffs of functional trie design is available at

http://www.nada.kth.se/~snilsson/publications/Functional-trie-compression-experiment/

An experimental study of compression methods for functional tries
Jukka-Pekka Iivonen, Stefan Nilsson, and Matti Tikkanen
WAAAPL'99

FWIW, apparently clojure uses a 32-ary hashtrie:

http://blog.ezyang.com/2010/03/the-case-of-the-hash-array-mapped-trie/
http://blog.higher-order.net/2009/09/08/understanding-clojures-persistenthashmap-deftwice/

Because it is only binary, Data.IntSet is sometimes quite deep. All of
that pointer chasing makes Data.Set actually faster than Data.IntSet
for looking up 0 in the set 0:[2^i | i <-[0..30]].