A general sequence representation with arbitrary annotations, with
example implementations of various collection types, 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://www.soi.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.
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