I've been contributing to an open source calculator, and I wanted a way to take integrals of functions. I suppose you could implement a definite integral function by using Riemann Sums, but I can't find any way to implement indefinite integrals (or derivatives for that matter). I've heard that functional programming is more adapt to abstract manipulation of mathematical models, for instance haskell, but I'm really not all too familiar with functionally programming at all. I'd like to stay within OOP. Does anyone know of any methods one could use to take indefinite integrals?