Rollable Expressions

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.9", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Rollable Expressions

Many games such as Dungeons & Dragons require rolling dice to determine the effects of player actions. You will build a program which makes it easier for players to automatically roll dice online.

Dice expressions are in the form 1d6 which means roll one six-sided die.

There can be any number of dice on the left hand side of the d and any number of sides on the dice on the right hand side of the d.

For example, 20d12 would roll twenty dice with twelve sides. 20d12.

Provided a text with a dice expression, replace the expression with a clickable link.

In markdown, a clickable link is in the format [link name](url).

Google allows you to roll multi sided dice by searching roll 1d6. The url for this is https://www.google.com/search?q=roll+1d6.

Rollable.replace("8d6")
"[8d6](https://www.google.com/search?q=roll+8d6)"

Ensure you handle 4, 6, 8, 12, and 20 sided dice and handle rolling between 1 and 99 dice.

Rollable.replace("Fireball: deal 8d6 fire damage.")
"Fireball: deal [8d6](https://www.google.com/search?q=roll+8d6) fire damage."

Bonus

Implement a Rollable.roll/1 function which finds rollable expressions and generates a random number based on the expression. For example, 1d6 would roll a single die returning a result from 1 to 6. 2d12 would generate two random numbers between 1 and 12 and add them together.

Rollable.roll("2d12")
"20"

Rollable.roll("2d12")
"24"

Rollable.roll("2d12")
"5"

Rollable.roll("Fireball: deal 8d6 fire damage.")
"Fireball: deal 20 fire damage."

Hint

You can use Regex.replace/4 to replace expressions in a string, and \d+ to match on one or more digits.

Example Solution

defmodule Rollable
  def replace(string) do
    Regex.replace(~r/(\d+)d(\d+)/, string, fn full, dice, sides ->
      "[#{full}](https://www.google.com/search?q=roll+#{dice}d#{sides})"
    end)
  end

  def roll(string) do
    Regex.replace(~r/(\d+)d(\d)+/, string, fn full, dice, sides ->
      dice_integer = String.to_integer(dice)
      sides_integer = String.to_integer(sides)

      value =
        1..dice_integer
        |> Enum.map(fn _ -> Enum.random(1..sides_integer) end)
        |> Enum.sum()
        |> Integer.to_string()
    end)
  end
end

Implement the Rollable module as documented below.

defmodule Rollable do
  @moduledoc """
  Documentation for `Rollable`
  """

  @doc """
  Replace dice expressions with clickable links.

  ## Examples

    iex> Rollable.replace("1d4")
    "[1d4](https://www.google.com/search?q=roll+1d4)"

    iex> Rollable.replace("1d6")
    "[1d6](https://www.google.com/search?q=roll+1d6)"

    iex> Rollable.replace("1d8")
    "[1d8](https://www.google.com/search?q=roll+1d8)"

    iex> Rollable.replace("1d12")
    "[1d12](https://www.google.com/search?q=roll+1d12)"

    iex> Rollable.replace("1d20")
    "[1d20](https://www.google.com/search?q=roll+1d20)"

    iex> Rollable.replace("8d6")
    "[8d6](https://www.google.com/search?q=roll+8d6)"

    iex> Rollable.replace("99d20")
    "[99d20](https://www.google.com/search?q=roll+99d20)"
    
    iex> Rollable.replace("Ice Shard: deal 12d4 ice damage.")
    "Ice Shard: deal [12d4](https://www.google.com/search?q=roll+12d4) ice damage."
  """
  def replace(string) do
    Regex.replace(~r/(\d+)d(\d+)/, string, fn full, dice, sides ->
      "[#{full}](https://www.google.com/search?q=roll+#{dice}d#{sides})"  
    end)    
  end

  def roll(string) do
    Regex.replace(~r/(\d+)d(\d)+/, string, fn _, dice, sides ->
      dice_integer = String.to_integer(dice)
      sides_integer = String.to_integer(sides)

      1..dice_integer
      |> Enum.map(fn _ -> Enum.random(1..sides_integer) end)
      |> Enum.sum()
      |> Integer.to_string()
    end)
  end
end

Rollable.roll("1d4")

Commit Your Progress

DockYard Academy now recommends you use the latest Release rather than forking or cloning our repository.

Run git status to ensure there are no undesirable changes. Then run the following in your command line from the curriculum folder to commit your progress.

$ git add .
$ git commit -m "finish Rollable Expressions exercise"
$ git push

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