jwlato:
Hello Günther,
I think the largest reason Haskellers don't use left-fold enumerators is that there isn't a ready-to-use package on Hackage. Oleg's code is extremely well commented and easy to follow, but it's not cabalized.
In addition to Takusen, Johan Tibbe's hyena application server uses enumerators for IO: http://github.com/tibbe/hyena/tree/master
There is a darcs repo of a cabalized iteratee package available at http://inmachina.net/~jwlato/haskell/iteratee/ This is essentially Oleg's code, slightly modified and reorganized. If anyone is interested in using left-fold enumerators for IO, please give it a look and let me know what you think. I'd like to put this on hackage in about a week or so, if possible. I would especially appreciate build reports.
There are a few iteratee/enumerator design questions that remain, which Oleg and others would like to explore more fully. The results of that research will likely find there way into this library.
I agree. There's no left-fold 'bytestring' equivalent. So it remains a special purpose technique. -- Don