[Haskell-cafe] Near Semi Ring problem

Dear Group, Many years ago I read a fascinating article which I can't seem to find anymore. It was about writing down (in english) the numbers from one to a billion? and being able to retrieve the nth letter. ie: onetwothreefourfive...ninehundredninetymillion....ninetynineonebillion I remember it used near semi rings and automatic differentiation, but no matter how I use those words to search (both google and duckduck) I can't find it. Do any of you have a pointer. I believe the code was written in haskell too. Best wishes, Henry Laxen