-module(functions_over_lists).

-export([product/1]).
-export([maximum/1]).
-export([product_fold/1]).

product(X) -> product(X, 1).
product([], Product) -> Product;
product([X | Xs], Product) -> product(Xs, X * Product).

product_fold(Xs) ->
  lists:foldl(fun(X, P) -> X * P end, 1, Xs).

% Return 'none' for empty lists
maximum([]) -> none;
% Initialize Max to the first list item
maximum([X | Xs]) -> maximum(Xs, X).
% When all items are exhausted, return held Max
maximum([], Max) -> Max;
% Replace Max when a list item is a number and larger than the current Max
maximum([X | Xs], Max) when is_number(X), X > Max -> maximum(Xs, X);
% Otherwise continue on to the next item
maximum([_ | Xs], Max) -> maximum(Xs, Max).