walking a directory tree efficiently

Hi.

During a tentative (quite unsuccessfull) to convert a simple Python 
script that prints on stdout a directory and all its subdirectory [1] in 
a good Haskell (mostly to start to do real practice with the language), 
I came across this blog post:
http://blog.moertel.com/articles/2007/03/28/directory-tree-printing-in-haskell-part-three-lazy-i-o

Since recently I read about alternatives to lazy IO (like iteratee), I'm 
curious to know if a flexible, efficient and safe alternative exists, 
for the task of display a directory tree.

[1] http://paste.pocoo.org/show/99523/

Thanks  Manlio perillo