A general sequence representation with arbitrary annotations, for use as a
base for implementations of various collection types, with examples, as
described in section 4 of

    Ralf Hinze and Ross Paterson, "Finger trees: a simple general-purpose
    data structure", Journal of Functional Programming 16:2 (2006) pp
    197-217. http://staff.city.ac.uk/~ross/papers/FingerTree.html

For a tuned sequence type, see Data.Sequence in the containers package,
which is a specialization of this structure.

Homepage:
http://hackage.haskell.org/package/hw-fingertree
