[Parsec] Extracting line and column numbers

Hi, I'm using the Parsec library to parse strings for a small experimental language. I'd like to decorate each node in the abstract syntax tree with a pair (Int, Int) that represents the line and column number in the strings. Unfortunately, the SourcePos class in the Parsec library is abstract and I cannot extract the line and column numbers from a SourcePos value. What are my options? With kind regards, Stefan Holdermans