Dear all, I am very pleased to announce the first release of splaytree. Splaytree provides splay tree based implementations of Sets, Seqs, and RangeSets. A RangeSet is similar to an IntervalSet, however as new ranges are inserted, they are combined with any existing ranges. This guarantees that the RangeSet consists of only non-overlapping ranges, and can be used to easily generate a list of non-overlapping ranges (read more at http://johnlato.blogspot.com/2011/09/splaytree-package-released.html). Absolute performance isn't a goal of this package, however according to my benchmarks it seems to be competitive with unordered-containers for many operations, although the worst-case complexity of a splay tree is O(n). http://hackage.haskell.org/package/splaytree repo: http://www.tiresiaspress.us/haskell/splaytree/ The design owes much to Ralf Hinze and Ross Paterson's excellent work on finger trees. John L.