Elixir deep_foldl

deep_foldl_test.exs

# # https://gist.github.com/ashneyderman/5c88439c68b19ecf50d5
# @type reducer :: (term, term -> term)
# @spec deep_foldl(list, term, reducer) :: term
#
# ## deep folds should accept arbitrarily deep nested lists
# ## it should call the fun on anything which is not a list.
# ## For a flat list, it should do the same thing as erlang's
# ## lists:foldl/3.
#
# 15 = deep_foldl([[1,[2,[3,[4,5]]]]], 0, fn(N,Sum) -> N+Sum end).
#
# %% Can you make it tail recursive?

ExUnit.start

defmodule DeepFoldlTest do
  use ExUnit.Case, async: true

  @type reducer :: (term, term -> term)
  @spec deep_foldl(list, term, reducer) :: term

  defp deep_foldl([], acc, _) do acc end

  defp deep_foldl([head | tail], acc, fun) when is_list(head) do
    deep_foldl(head ++ tail, acc, fun)
  end

  defp deep_foldl([head | tail], acc, fun) do
    deep_foldl(tail, fun.(head, acc), fun)
  end

  test "acceptance" do
    assert 15 == deep_foldl([[1,[2,[3,[4,5]]]]], 0, &+/2)
  end

  #test "nested multi element list" do
  #  assert 6 = deep_foldl([1,[2,3]], 0, &+/2)
  #end

  #test "first element nested list" do
  #  assert 3 = deep_foldl([[1],2], 0, &+/2)
  #end

  #test "empty list" do
  #  assert 3 == deep_foldl([], 3, &+/2)
  #end

  #test "simple list of integers" do
  #  assert 3 = deep_foldl([1,2], 0, &+/2)
  #end
end