angelikatyborska's solution to D&D Character on the Elixir track

Instructions

Test suite

Solution

For a game of Dungeons & Dragons, each player starts by generating a character they can play with. This character has, among other things, six abilities; strength, dexterity, constitution, intelligence, wisdom and charisma. These six abilities have scores that are determined randomly. You do this by rolling four 6-sided dice and record the sum of the largest three dice. You do this six times, once for each ability.

Your character's initial hitpoints are 10 + your character's constitution modifier. You find your character's constitution modifier by subtracting 10 from your character's constitution, divide by 2 and round down.

Write a random character generator that follows the rules above.

For example, the six throws of four dice may look like:

5, 3, 1, 6: You discard the 1 and sum 5 + 3 + 6 = 14, which you assign to strength.
3, 2, 5, 3: You discard the 2 and sum 3 + 5 + 3 = 11, which you assign to dexterity.
1, 1, 1, 1: You discard the 1 and sum 1 + 1 + 1 = 3, which you assign to constitution.
2, 1, 6, 6: You discard the 1 and sum 2 + 6 + 6 = 14, which you assign to intelligence.
3, 5, 3, 4: You discard the 3 and sum 5 + 3 + 4 = 12, which you assign to wisdom.
6, 6, 6, 6: You discard the 6 and sum 6 + 6 + 6 = 18, which you assign to charisma.

Because constitution is 3, the constitution modifier is -4 and the hitpoints are 6.

Notes

Most programming languages feature (pseudo-)random generators, but few programming languages are designed to roll dice. One such language is Troll.

dnd_character_test.exs

defmodule DndCharacterTest do
  use ExUnit.Case

  import DndCharacter, only: [modifier: 1, ability: 0, character: 0]

  # canonical data version: 1.1.0

  describe "ability modifier" do
    # @tag :pending
    test "for score 3 is -4" do
      assert modifier(3) === -4
    end

    @tag :pending
    test "for score 4 is -3" do
      assert modifier(4) === -3
    end

    @tag :pending
    test "for score 5 is -3" do
      assert modifier(5) === -3
    end

    @tag :pending
    test "for score 6 is -2" do
      assert modifier(6) === -2
    end

    @tag :pending
    test "for score 7 is -2" do
      assert modifier(7) === -2
    end

    @tag :pending
    test "for score 8 is -1" do
      assert modifier(8) === -1
    end

    @tag :pending
    test "for score 9 is -1" do
      assert modifier(9) === -1
    end

    @tag :pending
    test "for score 10 is 0" do
      assert modifier(10) === 0
    end

    @tag :pending
    test "for score 11 is 0" do
      assert modifier(11) === 0
    end

    @tag :pending
    test "for score 12 is +1" do
      assert modifier(12) === 1
    end

    @tag :pending
    test "for score 13 is +1" do
      assert modifier(13) === 1
    end

    @tag :pending
    test "for score 14 is +2" do
      assert modifier(14) === 2
    end

    @tag :pending
    test "for score 15 is +2" do
      assert modifier(15) === 2
    end

    @tag :pending
    test "for score 16 is +3" do
      assert modifier(16) === 3
    end

    @tag :pending
    test "for score 17 is +3" do
      assert modifier(17) === 3
    end

    @tag :pending
    test "for score 18 is +4" do
      assert modifier(18) === 4
    end
  end

  describe "random ability" do
    @tag :pending
    test "is within range" do
      Enum.each(1..200, fn _ -> assert ability() in 3..18 end)
    end
  end

  describe "random character" do
    setup do
      %{character: character()}
    end

    @tag :pending
    test "has valid hitpoints", %{character: character} do
      assert character.hitpoints === 10 + modifier(character.constitution)
    end

    @tag :pending
    test "has each ability only calculated once", %{character: character} do
      assert character.strength === character.strength
    end
  end
end

test_helper.exs

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

defmodule DndCharacter do
  @type t :: %__MODULE__{
          strength: pos_integer(),
          dexterity: pos_integer(),
          constitution: pos_integer(),
          intelligence: pos_integer(),
          wisdom: pos_integer(),
          charisma: pos_integer(),
          hitpoints: pos_integer()
        }

  defstruct ~w[strength dexterity constitution intelligence wisdom charisma hitpoints]a

  @spec modifier(pos_integer()) :: integer()
  def modifier(score) do
    Integer.floor_div(score - 10, 2)
  end

  @spec ability :: pos_integer()
  def ability do
    1..4
    |> Enum.map(fn _ -> k6_roll() end)
    |> Enum.sort()
    |> Enum.take(-3)
    |> Enum.sum()
  end

  @spec character :: t()
  def character do
    character = %__MODULE__{
      strength: ability(),
      dexterity: ability(),
      constitution: ability(),
      intelligence: ability(),
      wisdom: ability(),
      charisma: ability()
    }

    %{character | hitpoints: 10 + modifier(character.constitution)}
  end

  defp k6_roll() do
    :rand.uniform(6)
  end
end

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angelikatyborska's solution

to D&D Character in the Elixir Track

Notes

dnd_character_test.exs

test_helper.exs

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