[e-lang] 2-3 finger trees

[Dan Bornstein]

New-to-me data structure that may be of interest to the group:

     <http://www.soi.city.ac.uk/~ross/papers/FingerTree.html>

Abstract:

We present 2-3 finger trees, a functional representation of persistent 
sequences supporting access to the ends in amortized constant time, and 
concatenation and splitting in time logarithmic in the size of the 
smaller piece. Representations achieving these bounds have appeared 
previously, but 2-3 finger trees are much simpler, as are the operations 
on them. Further, by defining the split operation in a general form, we 
obtain a general purpose data structure that can serve as a sequence, 
priority queue, search tree, priority search queue and more.

-dan