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Learn Functional Programming with Elixir

Battling Through to the Exit

Develop our game further to include challenges for the player.

We'll cover the following...

Our game needs a challenge, or it won’t be fun. A challenge will reduce the chances of the player winning and let them feel like they overcame something when they do win.

For our challenge, we’ll implement a room with an enemy. The hero and the enemy will fight, and the first one to reach zero hit points is defeated. We need to build a list of enemies, create functions to reduce and restore character hit points, build a battle module, and create a room that can trigger a battle. Once we have a room-trigger contract, we need to follow it strictly.

The first step will be to construct a list of enemies, creating the lib/dungeon_crawl/enemies.ex file with the following code:

C++
defmodule DungeonCrawl.Enemies do 
  alias DungeonCrawl.Character
  def all, do: [ 
    %Character{
      name: "Ogre",
      description: "A large creature. Big muscles. Angry and hungry.", 
      hit_points: 12,
      max_hit_points: 12,
      damage_range: 3..5,
      attack_description: "a hammer"
    },
    %Character{
      name: "Orc",
      description: "A green evil creature. Wears armor and an axe.", 
      hit_points: 8,
      max_hit_points: 8,
      damage_range: 2..4,
      attack_description: "an axe"
    },
    %Character{
      name: "Goblin",
      description: "A small green creature. Wears dirty clothes and a dagger.", 
      hit_points: 4,
      max_hit_points: 4,
      damage_range: 1..2,
      attack_description: "a dagger"
    }, 
  ]
end

We’ve used the same DungeonCrawl.Character struct of the hero to create the enemies. It’s a list of suggested enemies. Feel free to create more or change the list. The next step is to create functions that permit the reduction or restoration of a character’s hit points and another function that displays the character’s current hit points. Let’s write these functions in the DungeonCrawl.Character module:

C++
defmodule DungeonCrawl.Character do 
  defstruct name: nil,
    description: nil, 
    hit_points: 0, 
    max_hit_points: 0, 
    attack_description: nil, 
    damage_range: nil
  defimpl String.Chars do
    def to_string(character), do: character.name
  end
  @type t :: %DungeonCrawl.Character{ 
    name: String.t,
    description: String.t, 
    hit_points: non_neg_integer, 
    max_hit_points: non_neg_integer, 
    attack_description: String.t, 
    damage_range: Range.t
  }
  def take_damage(character, damage) do
    new_hit_points = max(0, character.hit_points - damage) 
    %{character | hit_points: new_hit_points}
  end
  def heal(character, healing_value) do 
    new_hit_points = min(
      character.hit_points + healing_value,
      character.max_hit_points
    )
    %{character | hit_points: new_hit_points} 
  end
  def current_stats(character),
    do: "Player Stats\nHP: #{character.hit_points}/#{character.max_hit_points}"
end

The take_damage/2 function receives a character and the number of hit points ...