I've only just glanced at the source, but it seems to be based on the data structure explained on pg 77 of http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf http://

I've only just glanced at the source, but it seems to be based on the data structure explained on pg 77 of http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf.