There's a couple of great articles by dons on the innards as well (good explanation of how the zipper data structure simplifies things): http://cgi.cse.unsw.edu

There's a couple of great articles by dons on the innards as well (good explanation of how the zipper data structure simplifies things): http://cgi.cse.unsw.edu.au/~dons/blog/2007/05/01 http://cgi.cse.unsw.edu.au/~dons/blog/2007/05/01 http://cgi.cse.unsw.edu.au/~dons/blog/2007/05/17 http://cgi.cse.unsw.edu.au/~dons/blog/2007/05/17 (also http://cgi.cse.unsw.edu.au/~dons/blog/2007/06/02 http://cgi.cse.unsw.edu.au/~dons/blog/2007/06/02 )