[Haskell] Convert Expressions to....

[Scott West]

Hello all,
	I was just wondering if anyone had any ideas on how I could create an expression type to produce strings of some sort. So say I have something like (Exp a)  `oper` (Exp b), is there a way I could perform some operation on each left/right expression, and then on the whole expression? What I'm ultimately seeking is a way to turn expressions into mathML, or some similar sort of formatting. Thanks for any help you can provide!

Regards,
Scott