Many recursive functions share the same structure, e.g. pattern-match on the input and, depending on the data constructor, either recur on a smaller input or terminate the recursion with the base case. Another one: start with a seed value, use it to produce the first element of an infinite list, and recur on a modified seed in order to produce the rest of the list. Such a structure is called a recursion scheme. Using higher-order functions to implement those recursion schemes makes your code clearer, faster, and safer. See README for details.