The extra complexity is for dealing with extra data. Say you're mapping ByteString->Text. The iteratee reads one char, then says it's done. What do you do with

The extra complexity is for dealing with extra data. Say you're mapping ByteString->Text. The iteratee reads one char, then says it's done. What do you do with the extra bytes and text? Making them return a Step allows both types of extra input to be stored, and possibly consumed later by other iteratees. You can use (=$) or ($=) to modify how extra input is handled (by discarding it at certain points). Your wrapEnum is probably a special case of ($=).