Enum.map_join/3

defmodule Enum do
  def map_join(enumerable, joiner \\ "", fun)
end

Maps and joins the given enumerable in one pass.

joiner can be either a binary or a list and the result will be of the same type as joiner. If joiner is not passed at all, it defaults to an empty binary.

All elements returned from invoking the fun must be convertible to a binary, otherwise an error is raised.