basic_bench.exs

defmodule BasicBench do
  use Benchfella

  @num :random.uniform(999_999_999_999)

  bench "interpolation" do
    @num
    |> NumToWordsString.say
  end

  bench "list" do
    @num
    |> NumToWordsList.say
  end

  bench "iodata" do
    @num
    |> NumToWordsIOdata.say
  end
end

benchfella results

$ mix bench
Settings:
  duration:      1.0 s

## BasicBench
[15:03:21] 0/2: list
[15:03:24] 0/2: interpolation

Finished in 4.74 seconds

## BasicBench
list               500000   4.45 µs/op
interpolation       50000   32.73 µs/op

num_to_words_iodata.ex

defmodule NumToWordsIOdata do
  def say(number) when is_integer(number), do: to_word(number) |> IO.iodata_to_binary()
  def say(_), do: IO.puts "That's not a number"

  defp to_word(n) when n < 0, do: ["negative " | to_word(-n)]
  defp to_word(0), do: "zero"
  defp to_word(1), do: "one"
  defp to_word(2), do: "two"
  defp to_word(3), do: "three"
  defp to_word(4), do: "four"
  defp to_word(5), do: "five"
  defp to_word(6), do: "six"
  defp to_word(7), do: "seven"
  defp to_word(8), do: "eight"
  defp to_word(9), do: "nine"
  defp to_word(10), do: "ten"
  defp to_word(11), do: "eleven"
  defp to_word(12), do: "twelve"
  defp to_word(13), do: "thirteen"
  defp to_word(14), do: "fourteen"
  defp to_word(15), do: "fifteen"
  defp to_word(16), do: "sixteen"
  defp to_word(17), do: "seventeen"
  defp to_word(18), do: "eighteen"
  defp to_word(19), do: "nineteen"
  defp to_word(20), do: "twenty"
  defp to_word(30), do: "thirty"
  defp to_word(40), do: "forty"
  defp to_word(50), do: "fifty"
  defp to_word(60), do: "sixty"
  defp to_word(70), do: "seventy"
  defp to_word(80), do: "eighty"
  defp to_word(90), do: "ninety"
  defp to_word(n) when n < 100, do: [to_word(div(n,10)*10) | to_word_rem(n, 10)]
  defp to_word(n) when n < 1_000, do: [to_word(div(n,100)), " hundred" | to_word_rem(n, 100)]
  defp to_word(n) when n < 1_000_000, do: [to_word(div(n,1_000)), " thousand" | to_word_rem(n, 1_000)]
  defp to_word(n) when n < 1_000_000_000, do: [to_word(div(n,1_000_000)), " million" | to_word_rem(n, 1_000_000)]
  defp to_word(n) when n < 1_000_000_000_000, do: [to_word(div(n,1_000_000_000)), " billion" | to_word_rem(n, 1_000_000_000)]
  defp to_word(_), do: "I'm sorry, I can't count that high."

  defp to_word_rem(x, y) do
    case rem(x, y) do
      0 -> []
      z -> [?\s | to_word(z)]
    end
  end
end

num_to_words_list.ex

defmodule NumToWordsList do
  def say(0), do: "zero"
  def say(number) when is_integer(number), do: [to_word(number)] |> List.flatten |> Enum.reject(&Kernel.is_nil/1) |> Enum.join(" ")
  def say(_), do: IO.puts "That's not a number"

  defp to_word(n) when n < 0, do: ["negative", to_word(-n)]
  defp to_word(0), do: nil
  defp to_word(1), do: "one"
  defp to_word(2), do: "two"
  defp to_word(3), do: "three"
  defp to_word(4), do: "four"
  defp to_word(5), do: "five"
  defp to_word(6), do: "six"
  defp to_word(7), do: "seven"
  defp to_word(8), do: "eight"
  defp to_word(9), do: "nine"
  defp to_word(10), do: "ten"
  defp to_word(11), do: "eleven"
  defp to_word(12), do: "twelve"
  defp to_word(13), do: "thirteen"
  defp to_word(14), do: "fourteen"
  defp to_word(15), do: "fifteen"
  defp to_word(16), do: "sixteen"
  defp to_word(17), do: "seventeen"
  defp to_word(18), do: "eighteen"
  defp to_word(19), do: "nineteen"
  defp to_word(20), do: "twenty"
  defp to_word(30), do: "thirty"
  defp to_word(40), do: "forty"
  defp to_word(50), do: "fifty"
  defp to_word(60), do: "sixty"
  defp to_word(70), do: "seventy"
  defp to_word(80), do: "eighty"
  defp to_word(90), do: "ninety"
  defp to_word(n) when n < 100, do: [to_word(div(n,10)*10), to_word(rem(n, 10))]
  defp to_word(n) when n < 1_000, do: [to_word(div(n,100)), "hundred", to_word(rem(n, 100))]
  defp to_word(n) when n < 1_000_000, do: [to_word(div(n,1_000)), "thousand", to_word(rem(n, 1_000))]
  defp to_word(n) when n < 1_000_000_000, do: [to_word(div(n,1_000_000)), "million", to_word(rem(n, 1_000_000))]
  defp to_word(n) when n < 1_000_000_000_000, do: [to_word(div(n,1_000_000_000)), "billion", to_word(rem(n, 1_000_000_000))]
  defp to_word(_), do: "I'm sorry, I can't count that high."
end

num_to_words_string.ex

defmodule NumToWordsString do
  def say(0), do: "zero"
  def say(number) when is_integer(number), do: to_word(number) |> String.replace(~r/\s+/, " ") |> String.strip
  def say(_), do: IO.puts "That's not a number"

  defp to_word(n) when n < 0, do: "negative #{to_word(-n)}"
  defp to_word(0), do: ""
  defp to_word(1), do: "one"
  defp to_word(2), do: "two"
  defp to_word(3), do: "three"
  defp to_word(4), do: "four"
  defp to_word(5), do: "five"
  defp to_word(6), do: "six"
  defp to_word(7), do: "seven"
  defp to_word(8), do: "eight"
  defp to_word(9), do: "nine"
  defp to_word(10), do: "ten"
  defp to_word(11), do: "eleven"
  defp to_word(12), do: "twelve"
  defp to_word(13), do: "thirteen"
  defp to_word(14), do: "fourteen"
  defp to_word(15), do: "fifteen"
  defp to_word(16), do: "sixteen"
  defp to_word(17), do: "seventeen"
  defp to_word(18), do: "eighteen"
  defp to_word(19), do: "nineteen"
  defp to_word(20), do: "twenty"
  defp to_word(30), do: "thirty"
  defp to_word(40), do: "forty"
  defp to_word(50), do: "fifty"
  defp to_word(60), do: "sixty"
  defp to_word(70), do: "seventy"
  defp to_word(80), do: "eighty"
  defp to_word(90), do: "ninety"
  defp to_word(n) when n < 100, do: "#{to_word(div(n,10)*10)} #{to_word(rem(n, 10))}"
  defp to_word(n) when n < 1_000, do: "#{to_word(div(n,100))} hundred #{to_word(rem(n, 100))}"
  defp to_word(n) when n < 1_000_000, do: "#{to_word(div(n,1_000))} thousand #{to_word(rem(n, 1_000))}"
  defp to_word(n) when n < 1_000_000_000, do: "#{to_word(div(n,1_000_000))} million #{to_word(rem(n, 1_000_000))}"
  defp to_word(n) when n < 1_000_000_000_000, do: "#{to_word(div(n,1_000_000_000))} billion #{to_word(rem(n, 1_000_000_000))}"
  defp to_word(_), do: "I'm sorry, I can't count that high."
end