Eager streaming of XML/HTML data!
HTML::Mason (www.masonhq.com) is a Perl module that would make most Haskellers cringe. It is the most confused domain-specific-language you can see: Perl embedded in HTML.
But Mason is in wide use at amazon.com. In addition I just interviewed for a Perl poisition at the largest Oracle database installation in the world. And they are planning to move to Mason for HTML/XML/SOAP delivery... why would they do this? Because Mason can stream HTML data: instead of building up an entire XML document and then sending it, it can stream parts. When the document is _huge_ this becomes crucially important: render some of the xml, ship it off, reclaim the memory and keep on truckin'...
How could a lazy functional language achieve the design goal eagerly streaming data as opposed to lazily producing it on demand?