There is a great explanation of IO lists in Learn You Some Erlang [1], but in short — an IO list is functionally equivalent to a string builder, allowing you to

There is a great explanation of IO lists in Learn You Some Erlang [1], but in short — an IO list is functionally equivalent to a string builder, allowing you to accumulate individual strings in O(1) time. [1]: http://learnyousomeerlang.com/buckets-of-sockets http://learnyousomeerlang.com/buckets-of-sockets