Lazy Parsing

I'm wondering if there are any libraries out there for creating parsers that lazily build up their result. I know I could thread the remaining input through a parser by hand, but it seems like someone should have already done it. I'd like to be able to turn a stream of XML into a lazy tree of tags (probably Maybe tags, or Either errors tags), but I don't think HaXml and the like do that sort of thing. Branodn Moore