thekeele's solution to Beer Song on the Elixir track

Instructions

Test suite

Solution

Note:

This exercise has changed since this solution was written.

Recite the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.

Note that not all verses are identical.

99 bottles of beer on the wall, 99 bottles of beer.
Take one down and pass it around, 98 bottles of beer on the wall.

98 bottles of beer on the wall, 98 bottles of beer.
Take one down and pass it around, 97 bottles of beer on the wall.

97 bottles of beer on the wall, 97 bottles of beer.
Take one down and pass it around, 96 bottles of beer on the wall.

96 bottles of beer on the wall, 96 bottles of beer.
Take one down and pass it around, 95 bottles of beer on the wall.

95 bottles of beer on the wall, 95 bottles of beer.
Take one down and pass it around, 94 bottles of beer on the wall.

94 bottles of beer on the wall, 94 bottles of beer.
Take one down and pass it around, 93 bottles of beer on the wall.

93 bottles of beer on the wall, 93 bottles of beer.
Take one down and pass it around, 92 bottles of beer on the wall.

92 bottles of beer on the wall, 92 bottles of beer.
Take one down and pass it around, 91 bottles of beer on the wall.

91 bottles of beer on the wall, 91 bottles of beer.
Take one down and pass it around, 90 bottles of beer on the wall.

90 bottles of beer on the wall, 90 bottles of beer.
Take one down and pass it around, 89 bottles of beer on the wall.

89 bottles of beer on the wall, 89 bottles of beer.
Take one down and pass it around, 88 bottles of beer on the wall.

88 bottles of beer on the wall, 88 bottles of beer.
Take one down and pass it around, 87 bottles of beer on the wall.

87 bottles of beer on the wall, 87 bottles of beer.
Take one down and pass it around, 86 bottles of beer on the wall.

86 bottles of beer on the wall, 86 bottles of beer.
Take one down and pass it around, 85 bottles of beer on the wall.

85 bottles of beer on the wall, 85 bottles of beer.
Take one down and pass it around, 84 bottles of beer on the wall.

84 bottles of beer on the wall, 84 bottles of beer.
Take one down and pass it around, 83 bottles of beer on the wall.

83 bottles of beer on the wall, 83 bottles of beer.
Take one down and pass it around, 82 bottles of beer on the wall.

82 bottles of beer on the wall, 82 bottles of beer.
Take one down and pass it around, 81 bottles of beer on the wall.

81 bottles of beer on the wall, 81 bottles of beer.
Take one down and pass it around, 80 bottles of beer on the wall.

80 bottles of beer on the wall, 80 bottles of beer.
Take one down and pass it around, 79 bottles of beer on the wall.

79 bottles of beer on the wall, 79 bottles of beer.
Take one down and pass it around, 78 bottles of beer on the wall.

78 bottles of beer on the wall, 78 bottles of beer.
Take one down and pass it around, 77 bottles of beer on the wall.

77 bottles of beer on the wall, 77 bottles of beer.
Take one down and pass it around, 76 bottles of beer on the wall.

76 bottles of beer on the wall, 76 bottles of beer.
Take one down and pass it around, 75 bottles of beer on the wall.

75 bottles of beer on the wall, 75 bottles of beer.
Take one down and pass it around, 74 bottles of beer on the wall.

74 bottles of beer on the wall, 74 bottles of beer.
Take one down and pass it around, 73 bottles of beer on the wall.

73 bottles of beer on the wall, 73 bottles of beer.
Take one down and pass it around, 72 bottles of beer on the wall.

72 bottles of beer on the wall, 72 bottles of beer.
Take one down and pass it around, 71 bottles of beer on the wall.

71 bottles of beer on the wall, 71 bottles of beer.
Take one down and pass it around, 70 bottles of beer on the wall.

70 bottles of beer on the wall, 70 bottles of beer.
Take one down and pass it around, 69 bottles of beer on the wall.

69 bottles of beer on the wall, 69 bottles of beer.
Take one down and pass it around, 68 bottles of beer on the wall.

68 bottles of beer on the wall, 68 bottles of beer.
Take one down and pass it around, 67 bottles of beer on the wall.

67 bottles of beer on the wall, 67 bottles of beer.
Take one down and pass it around, 66 bottles of beer on the wall.

66 bottles of beer on the wall, 66 bottles of beer.
Take one down and pass it around, 65 bottles of beer on the wall.

65 bottles of beer on the wall, 65 bottles of beer.
Take one down and pass it around, 64 bottles of beer on the wall.

64 bottles of beer on the wall, 64 bottles of beer.
Take one down and pass it around, 63 bottles of beer on the wall.

63 bottles of beer on the wall, 63 bottles of beer.
Take one down and pass it around, 62 bottles of beer on the wall.

62 bottles of beer on the wall, 62 bottles of beer.
Take one down and pass it around, 61 bottles of beer on the wall.

61 bottles of beer on the wall, 61 bottles of beer.
Take one down and pass it around, 60 bottles of beer on the wall.

60 bottles of beer on the wall, 60 bottles of beer.
Take one down and pass it around, 59 bottles of beer on the wall.

59 bottles of beer on the wall, 59 bottles of beer.
Take one down and pass it around, 58 bottles of beer on the wall.

58 bottles of beer on the wall, 58 bottles of beer.
Take one down and pass it around, 57 bottles of beer on the wall.

57 bottles of beer on the wall, 57 bottles of beer.
Take one down and pass it around, 56 bottles of beer on the wall.

56 bottles of beer on the wall, 56 bottles of beer.
Take one down and pass it around, 55 bottles of beer on the wall.

55 bottles of beer on the wall, 55 bottles of beer.
Take one down and pass it around, 54 bottles of beer on the wall.

54 bottles of beer on the wall, 54 bottles of beer.
Take one down and pass it around, 53 bottles of beer on the wall.

53 bottles of beer on the wall, 53 bottles of beer.
Take one down and pass it around, 52 bottles of beer on the wall.

52 bottles of beer on the wall, 52 bottles of beer.
Take one down and pass it around, 51 bottles of beer on the wall.

51 bottles of beer on the wall, 51 bottles of beer.
Take one down and pass it around, 50 bottles of beer on the wall.

50 bottles of beer on the wall, 50 bottles of beer.
Take one down and pass it around, 49 bottles of beer on the wall.

49 bottles of beer on the wall, 49 bottles of beer.
Take one down and pass it around, 48 bottles of beer on the wall.

48 bottles of beer on the wall, 48 bottles of beer.
Take one down and pass it around, 47 bottles of beer on the wall.

47 bottles of beer on the wall, 47 bottles of beer.
Take one down and pass it around, 46 bottles of beer on the wall.

46 bottles of beer on the wall, 46 bottles of beer.
Take one down and pass it around, 45 bottles of beer on the wall.

45 bottles of beer on the wall, 45 bottles of beer.
Take one down and pass it around, 44 bottles of beer on the wall.

44 bottles of beer on the wall, 44 bottles of beer.
Take one down and pass it around, 43 bottles of beer on the wall.

43 bottles of beer on the wall, 43 bottles of beer.
Take one down and pass it around, 42 bottles of beer on the wall.

42 bottles of beer on the wall, 42 bottles of beer.
Take one down and pass it around, 41 bottles of beer on the wall.

41 bottles of beer on the wall, 41 bottles of beer.
Take one down and pass it around, 40 bottles of beer on the wall.

40 bottles of beer on the wall, 40 bottles of beer.
Take one down and pass it around, 39 bottles of beer on the wall.

39 bottles of beer on the wall, 39 bottles of beer.
Take one down and pass it around, 38 bottles of beer on the wall.

38 bottles of beer on the wall, 38 bottles of beer.
Take one down and pass it around, 37 bottles of beer on the wall.

37 bottles of beer on the wall, 37 bottles of beer.
Take one down and pass it around, 36 bottles of beer on the wall.

36 bottles of beer on the wall, 36 bottles of beer.
Take one down and pass it around, 35 bottles of beer on the wall.

35 bottles of beer on the wall, 35 bottles of beer.
Take one down and pass it around, 34 bottles of beer on the wall.

34 bottles of beer on the wall, 34 bottles of beer.
Take one down and pass it around, 33 bottles of beer on the wall.

33 bottles of beer on the wall, 33 bottles of beer.
Take one down and pass it around, 32 bottles of beer on the wall.

32 bottles of beer on the wall, 32 bottles of beer.
Take one down and pass it around, 31 bottles of beer on the wall.

31 bottles of beer on the wall, 31 bottles of beer.
Take one down and pass it around, 30 bottles of beer on the wall.

30 bottles of beer on the wall, 30 bottles of beer.
Take one down and pass it around, 29 bottles of beer on the wall.

29 bottles of beer on the wall, 29 bottles of beer.
Take one down and pass it around, 28 bottles of beer on the wall.

28 bottles of beer on the wall, 28 bottles of beer.
Take one down and pass it around, 27 bottles of beer on the wall.

27 bottles of beer on the wall, 27 bottles of beer.
Take one down and pass it around, 26 bottles of beer on the wall.

26 bottles of beer on the wall, 26 bottles of beer.
Take one down and pass it around, 25 bottles of beer on the wall.

25 bottles of beer on the wall, 25 bottles of beer.
Take one down and pass it around, 24 bottles of beer on the wall.

24 bottles of beer on the wall, 24 bottles of beer.
Take one down and pass it around, 23 bottles of beer on the wall.

23 bottles of beer on the wall, 23 bottles of beer.
Take one down and pass it around, 22 bottles of beer on the wall.

22 bottles of beer on the wall, 22 bottles of beer.
Take one down and pass it around, 21 bottles of beer on the wall.

21 bottles of beer on the wall, 21 bottles of beer.
Take one down and pass it around, 20 bottles of beer on the wall.

20 bottles of beer on the wall, 20 bottles of beer.
Take one down and pass it around, 19 bottles of beer on the wall.

19 bottles of beer on the wall, 19 bottles of beer.
Take one down and pass it around, 18 bottles of beer on the wall.

18 bottles of beer on the wall, 18 bottles of beer.
Take one down and pass it around, 17 bottles of beer on the wall.

17 bottles of beer on the wall, 17 bottles of beer.
Take one down and pass it around, 16 bottles of beer on the wall.

16 bottles of beer on the wall, 16 bottles of beer.
Take one down and pass it around, 15 bottles of beer on the wall.

15 bottles of beer on the wall, 15 bottles of beer.
Take one down and pass it around, 14 bottles of beer on the wall.

14 bottles of beer on the wall, 14 bottles of beer.
Take one down and pass it around, 13 bottles of beer on the wall.

13 bottles of beer on the wall, 13 bottles of beer.
Take one down and pass it around, 12 bottles of beer on the wall.

12 bottles of beer on the wall, 12 bottles of beer.
Take one down and pass it around, 11 bottles of beer on the wall.

11 bottles of beer on the wall, 11 bottles of beer.
Take one down and pass it around, 10 bottles of beer on the wall.

10 bottles of beer on the wall, 10 bottles of beer.
Take one down and pass it around, 9 bottles of beer on the wall.

9 bottles of beer on the wall, 9 bottles of beer.
Take one down and pass it around, 8 bottles of beer on the wall.

8 bottles of beer on the wall, 8 bottles of beer.
Take one down and pass it around, 7 bottles of beer on the wall.

7 bottles of beer on the wall, 7 bottles of beer.
Take one down and pass it around, 6 bottles of beer on the wall.

6 bottles of beer on the wall, 6 bottles of beer.
Take one down and pass it around, 5 bottles of beer on the wall.

5 bottles of beer on the wall, 5 bottles of beer.
Take one down and pass it around, 4 bottles of beer on the wall.

4 bottles of beer on the wall, 4 bottles of beer.
Take one down and pass it around, 3 bottles of beer on the wall.

3 bottles of beer on the wall, 3 bottles of beer.
Take one down and pass it around, 2 bottles of beer on the wall.

2 bottles of beer on the wall, 2 bottles of beer.
Take one down and pass it around, 1 bottle of beer on the wall.

1 bottle of beer on the wall, 1 bottle of beer.
Take it down and pass it around, no more bottles of beer on the wall.

No more bottles of beer on the wall, no more bottles of beer.
Go to the store and buy some more, 99 bottles of beer on the wall.

For bonus points

Did you get the tests passing and the code clean? If you want to, these are some additional things you could try:

Remove as much duplication as you possibly can.
Optimize for readability, even if it means introducing duplication.
If you've removed all the duplication, do you have a lot of conditionals? Try replacing the conditionals with polymorphism, if it applies in this language. How readable is it?

Then please share your thoughts in a comment on the submission. Did this experiment make the code better? Worse? Did you learn anything from it?

Running tests

Execute the tests with:

$ elixir beer_song_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

Learn to Program by Chris Pine http://pine.fm/LearnToProgram/?Chapter=06

Submitting Incomplete Solutions

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

beer_song_test.exs

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

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

defmodule BeerSongTest do
  use ExUnit.Case

  test "getting the first verse (99 bottles)" do
    assert BeerSong.verse(99) == """
           99 bottles of beer on the wall, 99 bottles of beer.
           Take one down and pass it around, 98 bottles of beer on the wall.
           """
  end

  @tag :pending
  test "getting the second verse (98 bottles)" do
    assert BeerSong.verse(98) == """
           98 bottles of beer on the wall, 98 bottles of beer.
           Take one down and pass it around, 97 bottles of beer on the wall.
           """
  end

  @tag :pending
  test "getting just the penultimate verse" do
    assert BeerSong.verse(1) == """
           1 bottle of beer on the wall, 1 bottle of beer.
           Take it down and pass it around, no more bottles of beer on the wall.
           """
  end

  @tag :pending
  test "getting just the last verse" do
    assert BeerSong.verse(0) == """
           No more bottles of beer on the wall, no more bottles of beer.
           Go to the store and buy some more, 99 bottles of beer on the wall.
           """
  end

  @tag :pending
  test "getting the last 4 verses" do
    assert BeerSong.lyrics(3..0) == """
           3 bottles of beer on the wall, 3 bottles of beer.
           Take one down and pass it around, 2 bottles of beer on the wall.

           2 bottles of beer on the wall, 2 bottles of beer.
           Take one down and pass it around, 1 bottle of beer on the wall.

           1 bottle of beer on the wall, 1 bottle of beer.
           Take it down and pass it around, no more bottles of beer on the wall.

           No more bottles of beer on the wall, no more bottles of beer.
           Go to the store and buy some more, 99 bottles of beer on the wall.
           """
  end

  @tag :pending
  test "getting the whole song" do
    assert BeerSong.lyrics() == """
           99 bottles of beer on the wall, 99 bottles of beer.
           Take one down and pass it around, 98 bottles of beer on the wall.

           98 bottles of beer on the wall, 98 bottles of beer.
           Take one down and pass it around, 97 bottles of beer on the wall.

           97 bottles of beer on the wall, 97 bottles of beer.
           Take one down and pass it around, 96 bottles of beer on the wall.

           96 bottles of beer on the wall, 96 bottles of beer.
           Take one down and pass it around, 95 bottles of beer on the wall.

           95 bottles of beer on the wall, 95 bottles of beer.
           Take one down and pass it around, 94 bottles of beer on the wall.

           94 bottles of beer on the wall, 94 bottles of beer.
           Take one down and pass it around, 93 bottles of beer on the wall.

           93 bottles of beer on the wall, 93 bottles of beer.
           Take one down and pass it around, 92 bottles of beer on the wall.

           92 bottles of beer on the wall, 92 bottles of beer.
           Take one down and pass it around, 91 bottles of beer on the wall.

           91 bottles of beer on the wall, 91 bottles of beer.
           Take one down and pass it around, 90 bottles of beer on the wall.

           90 bottles of beer on the wall, 90 bottles of beer.
           Take one down and pass it around, 89 bottles of beer on the wall.

           89 bottles of beer on the wall, 89 bottles of beer.
           Take one down and pass it around, 88 bottles of beer on the wall.

           88 bottles of beer on the wall, 88 bottles of beer.
           Take one down and pass it around, 87 bottles of beer on the wall.

           87 bottles of beer on the wall, 87 bottles of beer.
           Take one down and pass it around, 86 bottles of beer on the wall.

           86 bottles of beer on the wall, 86 bottles of beer.
           Take one down and pass it around, 85 bottles of beer on the wall.

           85 bottles of beer on the wall, 85 bottles of beer.
           Take one down and pass it around, 84 bottles of beer on the wall.

           84 bottles of beer on the wall, 84 bottles of beer.
           Take one down and pass it around, 83 bottles of beer on the wall.

           83 bottles of beer on the wall, 83 bottles of beer.
           Take one down and pass it around, 82 bottles of beer on the wall.

           82 bottles of beer on the wall, 82 bottles of beer.
           Take one down and pass it around, 81 bottles of beer on the wall.

           81 bottles of beer on the wall, 81 bottles of beer.
           Take one down and pass it around, 80 bottles of beer on the wall.

           80 bottles of beer on the wall, 80 bottles of beer.
           Take one down and pass it around, 79 bottles of beer on the wall.

           79 bottles of beer on the wall, 79 bottles of beer.
           Take one down and pass it around, 78 bottles of beer on the wall.

           78 bottles of beer on the wall, 78 bottles of beer.
           Take one down and pass it around, 77 bottles of beer on the wall.

           77 bottles of beer on the wall, 77 bottles of beer.
           Take one down and pass it around, 76 bottles of beer on the wall.

           76 bottles of beer on the wall, 76 bottles of beer.
           Take one down and pass it around, 75 bottles of beer on the wall.

           75 bottles of beer on the wall, 75 bottles of beer.
           Take one down and pass it around, 74 bottles of beer on the wall.

           74 bottles of beer on the wall, 74 bottles of beer.
           Take one down and pass it around, 73 bottles of beer on the wall.

           73 bottles of beer on the wall, 73 bottles of beer.
           Take one down and pass it around, 72 bottles of beer on the wall.

           72 bottles of beer on the wall, 72 bottles of beer.
           Take one down and pass it around, 71 bottles of beer on the wall.

           71 bottles of beer on the wall, 71 bottles of beer.
           Take one down and pass it around, 70 bottles of beer on the wall.

           70 bottles of beer on the wall, 70 bottles of beer.
           Take one down and pass it around, 69 bottles of beer on the wall.

           69 bottles of beer on the wall, 69 bottles of beer.
           Take one down and pass it around, 68 bottles of beer on the wall.

           68 bottles of beer on the wall, 68 bottles of beer.
           Take one down and pass it around, 67 bottles of beer on the wall.

           67 bottles of beer on the wall, 67 bottles of beer.
           Take one down and pass it around, 66 bottles of beer on the wall.

           66 bottles of beer on the wall, 66 bottles of beer.
           Take one down and pass it around, 65 bottles of beer on the wall.

           65 bottles of beer on the wall, 65 bottles of beer.
           Take one down and pass it around, 64 bottles of beer on the wall.

           64 bottles of beer on the wall, 64 bottles of beer.
           Take one down and pass it around, 63 bottles of beer on the wall.

           63 bottles of beer on the wall, 63 bottles of beer.
           Take one down and pass it around, 62 bottles of beer on the wall.

           62 bottles of beer on the wall, 62 bottles of beer.
           Take one down and pass it around, 61 bottles of beer on the wall.

           61 bottles of beer on the wall, 61 bottles of beer.
           Take one down and pass it around, 60 bottles of beer on the wall.

           60 bottles of beer on the wall, 60 bottles of beer.
           Take one down and pass it around, 59 bottles of beer on the wall.

           59 bottles of beer on the wall, 59 bottles of beer.
           Take one down and pass it around, 58 bottles of beer on the wall.

           58 bottles of beer on the wall, 58 bottles of beer.
           Take one down and pass it around, 57 bottles of beer on the wall.

           57 bottles of beer on the wall, 57 bottles of beer.
           Take one down and pass it around, 56 bottles of beer on the wall.

           56 bottles of beer on the wall, 56 bottles of beer.
           Take one down and pass it around, 55 bottles of beer on the wall.

           55 bottles of beer on the wall, 55 bottles of beer.
           Take one down and pass it around, 54 bottles of beer on the wall.

           54 bottles of beer on the wall, 54 bottles of beer.
           Take one down and pass it around, 53 bottles of beer on the wall.

           53 bottles of beer on the wall, 53 bottles of beer.
           Take one down and pass it around, 52 bottles of beer on the wall.

           52 bottles of beer on the wall, 52 bottles of beer.
           Take one down and pass it around, 51 bottles of beer on the wall.

           51 bottles of beer on the wall, 51 bottles of beer.
           Take one down and pass it around, 50 bottles of beer on the wall.

           50 bottles of beer on the wall, 50 bottles of beer.
           Take one down and pass it around, 49 bottles of beer on the wall.

           49 bottles of beer on the wall, 49 bottles of beer.
           Take one down and pass it around, 48 bottles of beer on the wall.

           48 bottles of beer on the wall, 48 bottles of beer.
           Take one down and pass it around, 47 bottles of beer on the wall.

           47 bottles of beer on the wall, 47 bottles of beer.
           Take one down and pass it around, 46 bottles of beer on the wall.

           46 bottles of beer on the wall, 46 bottles of beer.
           Take one down and pass it around, 45 bottles of beer on the wall.

           45 bottles of beer on the wall, 45 bottles of beer.
           Take one down and pass it around, 44 bottles of beer on the wall.

           44 bottles of beer on the wall, 44 bottles of beer.
           Take one down and pass it around, 43 bottles of beer on the wall.

           43 bottles of beer on the wall, 43 bottles of beer.
           Take one down and pass it around, 42 bottles of beer on the wall.

           42 bottles of beer on the wall, 42 bottles of beer.
           Take one down and pass it around, 41 bottles of beer on the wall.

           41 bottles of beer on the wall, 41 bottles of beer.
           Take one down and pass it around, 40 bottles of beer on the wall.

           40 bottles of beer on the wall, 40 bottles of beer.
           Take one down and pass it around, 39 bottles of beer on the wall.

           39 bottles of beer on the wall, 39 bottles of beer.
           Take one down and pass it around, 38 bottles of beer on the wall.

           38 bottles of beer on the wall, 38 bottles of beer.
           Take one down and pass it around, 37 bottles of beer on the wall.

           37 bottles of beer on the wall, 37 bottles of beer.
           Take one down and pass it around, 36 bottles of beer on the wall.

           36 bottles of beer on the wall, 36 bottles of beer.
           Take one down and pass it around, 35 bottles of beer on the wall.

           35 bottles of beer on the wall, 35 bottles of beer.
           Take one down and pass it around, 34 bottles of beer on the wall.

           34 bottles of beer on the wall, 34 bottles of beer.
           Take one down and pass it around, 33 bottles of beer on the wall.

           33 bottles of beer on the wall, 33 bottles of beer.
           Take one down and pass it around, 32 bottles of beer on the wall.

           32 bottles of beer on the wall, 32 bottles of beer.
           Take one down and pass it around, 31 bottles of beer on the wall.

           31 bottles of beer on the wall, 31 bottles of beer.
           Take one down and pass it around, 30 bottles of beer on the wall.

           30 bottles of beer on the wall, 30 bottles of beer.
           Take one down and pass it around, 29 bottles of beer on the wall.

           29 bottles of beer on the wall, 29 bottles of beer.
           Take one down and pass it around, 28 bottles of beer on the wall.

           28 bottles of beer on the wall, 28 bottles of beer.
           Take one down and pass it around, 27 bottles of beer on the wall.

           27 bottles of beer on the wall, 27 bottles of beer.
           Take one down and pass it around, 26 bottles of beer on the wall.

           26 bottles of beer on the wall, 26 bottles of beer.
           Take one down and pass it around, 25 bottles of beer on the wall.

           25 bottles of beer on the wall, 25 bottles of beer.
           Take one down and pass it around, 24 bottles of beer on the wall.

           24 bottles of beer on the wall, 24 bottles of beer.
           Take one down and pass it around, 23 bottles of beer on the wall.

           23 bottles of beer on the wall, 23 bottles of beer.
           Take one down and pass it around, 22 bottles of beer on the wall.

           22 bottles of beer on the wall, 22 bottles of beer.
           Take one down and pass it around, 21 bottles of beer on the wall.

           21 bottles of beer on the wall, 21 bottles of beer.
           Take one down and pass it around, 20 bottles of beer on the wall.

           20 bottles of beer on the wall, 20 bottles of beer.
           Take one down and pass it around, 19 bottles of beer on the wall.

           19 bottles of beer on the wall, 19 bottles of beer.
           Take one down and pass it around, 18 bottles of beer on the wall.

           18 bottles of beer on the wall, 18 bottles of beer.
           Take one down and pass it around, 17 bottles of beer on the wall.

           17 bottles of beer on the wall, 17 bottles of beer.
           Take one down and pass it around, 16 bottles of beer on the wall.

           16 bottles of beer on the wall, 16 bottles of beer.
           Take one down and pass it around, 15 bottles of beer on the wall.

           15 bottles of beer on the wall, 15 bottles of beer.
           Take one down and pass it around, 14 bottles of beer on the wall.

           14 bottles of beer on the wall, 14 bottles of beer.
           Take one down and pass it around, 13 bottles of beer on the wall.

           13 bottles of beer on the wall, 13 bottles of beer.
           Take one down and pass it around, 12 bottles of beer on the wall.

           12 bottles of beer on the wall, 12 bottles of beer.
           Take one down and pass it around, 11 bottles of beer on the wall.

           11 bottles of beer on the wall, 11 bottles of beer.
           Take one down and pass it around, 10 bottles of beer on the wall.

           10 bottles of beer on the wall, 10 bottles of beer.
           Take one down and pass it around, 9 bottles of beer on the wall.

           9 bottles of beer on the wall, 9 bottles of beer.
           Take one down and pass it around, 8 bottles of beer on the wall.

           8 bottles of beer on the wall, 8 bottles of beer.
           Take one down and pass it around, 7 bottles of beer on the wall.

           7 bottles of beer on the wall, 7 bottles of beer.
           Take one down and pass it around, 6 bottles of beer on the wall.

           6 bottles of beer on the wall, 6 bottles of beer.
           Take one down and pass it around, 5 bottles of beer on the wall.

           5 bottles of beer on the wall, 5 bottles of beer.
           Take one down and pass it around, 4 bottles of beer on the wall.

           4 bottles of beer on the wall, 4 bottles of beer.
           Take one down and pass it around, 3 bottles of beer on the wall.

           3 bottles of beer on the wall, 3 bottles of beer.
           Take one down and pass it around, 2 bottles of beer on the wall.

           2 bottles of beer on the wall, 2 bottles of beer.
           Take one down and pass it around, 1 bottle of beer on the wall.

           1 bottle of beer on the wall, 1 bottle of beer.
           Take it down and pass it around, no more bottles of beer on the wall.

           No more bottles of beer on the wall, no more bottles of beer.
           Go to the store and buy some more, 99 bottles of beer on the wall.
           """
  end
end

defmodule BeerSong do
  @doc """
  Get a single verse of the beer song
  """

  @spec verse(integer) :: String.t()
  def verse(0) do
    """
    No more bottles of beer on the wall, no more bottles of beer.
    Go to the store and buy some more, 99 bottles of beer on the wall.
    """
  end
  def verse(number) do
    """
    #{bottles_of_beer(number)} on the wall, #{bottles_of_beer(number)}.
    Take #{beer(number - 1)} down and pass it around, #{bottles_of_beer(number - 1)} on the wall.
    """
  end

  defp bottles_of_beer(bottles) when bottles > 1, do: "#{bottles} bottles of beer"
  defp bottles_of_beer(1), do: "1 bottle of beer"
  defp bottles_of_beer(0), do: "no more bottles of beer"

  defp beer(beer) when beer > 0, do: "one"
  defp beer(0), do: "it"

  @doc """
  Get the entire beer song for a given range of numbers of bottles.
  """
  @spec lyrics(Range.t()) :: String.t()
  def lyrics(range \\ 99..0) do
    Enum.map_join(range, "\n", &verse/1)
  end
end

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thekeele's solution

to Beer Song in the Elixir Track