Demonstrates funky fn name mangling and my own confusion with Dict.merge/3 docs.

merge-problem.exs

defmodule MergeProblem do
  def count(string) do
    words = String.split(string)
      |> Enum.reject(&1 == "")
      |> Enum.map(&String.downcase/1)
    count = HashDict.new(words, fn key -> {key, 0} end)
    count = HashDict.merge(count, words, fn _k, v1, _v2 -> v1 + 1 end)
    count
  end

  # Yields error:
  # word-count% iex
  # Erlang R16B01 (erts-5.10.2) [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]
  # 
  # Interactive Elixir (0.10.1) - press Ctrl+C to exit (type h() ENTER for help)
  # iex(1)> c("merge-problem.exs", ".")
  # {{path}}/word-count/merge-problem.exs:1: redefining module MergeProblem
  # [MergeProblem]
  # iex(2)> MergeProblem.test()
  # ** (FunctionClauseError) no function clause matching in HashDict."-merge/3-fun-5-"/2
  #     /private/tmp/elixir-wnuv/elixir-0.10.1/lib/elixir/lib/hash_dict.ex:215: HashDict."-merge/3-fun-5-"("test", #HashDict<[{"a", 0}, {"is", 0}, {"test", 0}, {"this", 0}]>)
  #     /private/tmp/elixir-wnuv/elixir-0.10.1/lib/elixir/lib/enum.ex:1522: Enumerable.List.reduce/3
  #     erl_eval.erl:569: :erl_eval.do_apply/6
  #     src/elixir.erl:147: :elixir.eval_forms/3
  def test() do
    count("test this is a test")
  end
end