“in computation there are two phases: generating data and transforming data. This function is very clearly performing a transformation on data, while the fibonacci function generates it. This clear demarcation adds extra clarity and extra functionality: we can move a transformative function to work on a new set of data, or perform multiple transformations on existing data. This paradigm has always been important when creating complex programs; however, generators facilitate this clearly by making generators responsible for creating the data, and normal functions responsible for acting on the generated data.”