Mostly these days I suppose I'm known for MathML and XSLT stuff. Before that I used TeX rather a lot (I must check one of these days whether I have yet posted as often to xsl-list as I have to comp.text.tex). Around the time I started to use TeX (1987 or thereabouts) I was mainly programming in the functional programming language Standard ML. I haven't done so much with ML since, but the ML family of languages have been having something of a renaissance recently, especially with Microsoft's F# language.
So I've been returning to my roots and doing a bit of functional programming over the last few days, writing an article hosted at NAG on calling the NAG library from F#.