This library is designed to be a drop-in replacement for the Haskell
Data.Sequence library from the containers package, originally written
by Ross Patterson and Ralf Hinze and documented here:

http://hackage.haskell.org/packages/archive/containers/0.4.2.1/doc/html/Data-Sequence.html

Like Data.Sequence, Data.FastSequence makes use of finger trees in
order to provide O(lg n) concatenation and indexing.  However, it uses
much wider vector-style nodes rather than the 2-3 tree nodes used in
Data.Sequence.  It is intended to run faster in practice than
Data.Sequence; substantial performance regressions should be
considered a bug.

For now, though, the code is still under development and testing.