List.flatten reimplementation in elixir.

my_list.ex

defmodule MyList do

	def flatten(array) do
		reduce_flatten(array, [])
	end

	def reduce_flatten([], acc), do: acc

	def reduce_flatten([elem | rest], acc) do
		Enum.reduce([elem | rest], acc, &reduce_flatten/2)
	end

	def reduce_flatten(elem, acc) do
		acc ++ [elem]
	end

end

my_list_test.exs

defmodule MyListTest do
	use ExUnit.Case
	doctest MyList

	test "flatten empty array" do
		assert MyList.flatten([]) == []
	end

	test "flattened array stays unchanged" do
		assert MyList.flatten([1,2,3]) == [1,2,3]
	end

	test "flatten simple nested" do
		assert MyList.flatten([1,[2],3]) == [1,2,3]
	end

	test "flatten messy nested array" do
		assert MyList.flatten([[[],[2,3,[4]]], [5,6], [[[7]]]]) == [2,3,4,5,6,7]
	end

end