[Haskell-cafe] cumulative sum

Hi, I have two lists, p and lambda (both are finite). I would like to calculate 1) the cumulative sum of lambda, ie if lambda = [lambda1,lambda2,lambda3,...] then csum lambda = [lambda1,lambda1+lambda2,lambda1+lambda2+lambda3,...] 2) the cumulative sum of p*lambda (multiplication elementwise) Once I know how to do the first, I know how to do the second I guess (doing the multiplication using zipWith to get the p*lambda list, but I would be interested in any other suggestions). Currently I take and sum, but then I am calculating the same sums many times. Thanks, Tamas