[Haskell-cafe] Pretty printing HTML

Hi, I want to pretty print some text as HTML, using the standard HughesPJ combinators. The problem is that I want the "length" of a text string to be its textual context, not its character length. For example, a keyword will display as "case", but internally will be the string "<span class='keyword'>case</span>" Is there any way to acheive this? I have come up with something, but its not nice at all. It basically involves parsing the generated text and inserting the extra HTML back in. Thanks Neil