Avatar of paulfioravanti

paulfioravanti's solution

to Twelve Days in the Elixir Track

Published at Jun 20 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Output the lyrics to 'The Twelve Days of Christmas'.

On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.

On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.

On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.

Running tests

Execute the tests with:

$ elixir twelve_days_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

Source

Wikipedia http://en.wikipedia.org/wiki/The_Twelve_Days_of_Christmas_(song)

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

twelve_days_test.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("twelve_days.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(trace: true, exclude: :pending)

defmodule TwelveDaysTest do
  use ExUnit.Case

  describe "verse" do
    # @tag :pending
    test "first verse" do
      assert TwelveDays.verse(1) ==
               "On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree."
    end

    @tag :pending
    test "sixth verse" do
      assert TwelveDays.verse(6) ==
               "On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."
    end

    @tag :pending
    test "last verse" do
      assert TwelveDays.verse(12) ==
               "On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."
    end
  end

  describe "verses" do
    @tag :pending
    test "1-3" do
      assert TwelveDays.verses(1, 3) ==
               """
               On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.
               On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.
               On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               """
               |> String.trim()
    end

    @tag :pending
    test "4-6" do
      assert TwelveDays.verses(4, 6) ==
               """
               On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               """
               |> String.trim()
    end

    @tag :pending
    test "1-12" do
      assert TwelveDays.verses(1, 12) ==
               """
               On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.
               On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.
               On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               """
               |> String.trim()
    end
  end

  describe "sing" do
    @tag :pending
    test "all 12 verses" do
      assert TwelveDays.sing() ==
               """
               On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.
               On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.
               On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
               """
               |> String.trim()
    end
  end
end
defmodule TwelveDays do
  @cardinals %{
    "first" => "a",
    "second" => "two",
    "third" => "three",
    "fifth" => "five",
    "eighth" => "eight",
    "ninth" => "nine",
    "twelfth" => "twelve"
  }
  @comma ", "
  @comma_and ", and "
  @day_placeholder "{day}"
  @declaration_of_receipt "On the " <>
                            @day_placeholder <>
                            " day of Christmas my true love gave to me: "

  @gifts [
    " Partridge in a Pear Tree",
    " Turtle Doves",
    " French Hens",
    " Calling Birds",
    " Gold Rings",
    " Geese-a-Laying",
    " Swans-a-Swimming",
    " Maids-a-Milking",
    " Ladies Dancing",
    " Lords-a-Leaping",
    " Pipers Piping",
    " Drummers Drumming"
  ]
  @ordinals ~w(
    first
    second
    third
    fourth
    fifth
    sixth
    seventh
    eighth
    ninth
    tenth
    eleventh
    twelfth
  )
  @gifts_for_each_day_of_christmas Enum.zip(@ordinals, @gifts)
  @ordinal_ending ~r/th\z/
  @newline "\n"
  @period "."

  @doc """
  Given a `number`, return the song's verse for that specific day, including
  all gifts for previous days in the same line.
  """
  @spec verse(number :: integer) :: String.t()
  def verse(number) do
    index = number - 1
    ordinal = Enum.at(@ordinals, index)
    amount = cardinal_from_ordinal(ordinal)
    current_gift = Enum.at(@gifts, index)
    extra_gifts = calculate_extra_gifts(index)

    @declaration_of_receipt
    |> String.replace(@day_placeholder, ordinal)
    |> Kernel.<>(amount)
    |> Kernel.<>(current_gift)
    |> Kernel.<>(extra_gifts)
    |> Kernel.<>(@period)
  end

  @doc """
  Given a `starting_verse` and an `ending_verse`, return the verses for each
  included day, one per line.
  """
  @spec verses(starting_verse :: integer, ending_verse :: integer) :: String.t()
  def verses(starting_verse, ending_verse) do
    starting_verse..ending_verse
    |> Enum.map(&verse/1)
    |> Enum.join(@newline)
  end

  @doc """
  Sing all 12 verses, in order, one verse per line.
  """
  @spec sing() :: String.t()
  def sing do
    verses(1, 12)
  end

  defp cardinal_from_ordinal(ordinal) do
    @cardinals
    |> Map.get(ordinal, remove_ordinal_ending(ordinal))
  end

  defp remove_ordinal_ending(ordinal) do
    ordinal
    |> String.replace(@ordinal_ending, "")
  end

  defp calculate_extra_gifts(index) do
    @gifts_for_each_day_of_christmas
    |> Enum.take(index)
    |> Enum.reduce([], &add_gift/2)
    |> Enum.join()
  end

  defp add_gift({ordinal, gift}, acc) do
    amount = cardinal_from_ordinal(ordinal)

    case acc do
      [] ->
        [@comma_and <> amount <> gift]

      _ ->
        [@comma <> amount <> gift | acc]
    end
  end
end

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?