Edison is a library of purely functional data structures written by Chris
Okasaki.  It is named after Thomas Alva Edison and for the mnemonic value
EDiSon (Efficient Data Structures).  Edison provides several families of
abstractions, each with multiple implementations.  The main abstractions
provided by Edison are: Sequences such as stacks, queues, and dequeues;
Collections such as sets, bags and heaps; and Associative Collections such
as finite maps and priority queues where the priority and element are
distinct.

WWW: http://rwd.rdockins.name/edison/home/