Math With Guards

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Math

In this exercise, you’re going to use guards to create a Math module that handles adding and subtracting integers, strings, and lists. You do not need to handling adding or subtracting different data types.

Math.add(1, 2)
3

Math.add("Hello, ", "World!")
"Hello, World!"

Math.add([1, 2], [3, 4])
[1, 2, 3, 4]

Math.subtract(10, 2)
8

Math.subtract("hello there", "hello ")
"there"

Math.subtract([1, 2, 3, 4], [1, 3])
[2, 4]

Hint: Subtracting Strings

Consider converting your strings to a list, then subtract the two lists together then join your result back into a string.

Example Solution

defmodule Math do
  def add(integer1, integer2) when is_integer(integer1) and is_integer(integer2) do
    integer1 + integer2
  end

  def add(list1, list2) when is_list(list1) and is_list(list2) do
    list1 ++ list2
  end

  def add(string1, string2) when is_binary(string1) and is_binary(string2) do
    string1 <> string2
  end

  def subtract(integer1, integer2) when is_integer(integer1) and is_integer(integer2) do
    integer1 - integer2
  end

  def subtract(list1, list2) when is_list(list1) and is_list(list2) do
    list1 -- list2
  end

  def subtract(string1, string2) when is_binary(string1) and is_binary(string2) do
    String.split(string1, "")
    |> subtract(String.split(string2, ""))
    |> Enum.join()
  end
end

Implement the Math module as documented below.

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

  @doc """
  Add two integers, strings, or lists.

  ## Examples

    iex> Math.add(2, 2)
    4
    iex> Math.add(4, 4)
    8

    Math.add([1, 2], [3, 4])
    [1, 2, 3, 4]
    Math.add([1, 2, 3], [4, 5, 6])
    [1, 2, 3, 4, 5, 6]

    iex> Math.add("abc", "def")
    "abcdef"
    iex> Math.add("123", "456")
    "123456"

    iex> Math.add(1.0, 2.0)
    ** (FunctionClauseError) no function clause matching in Math.add/2

    iex> Math.add(2, "2")
    ** (FunctionClauseError) no function clause matching in Math.add/2

    iex> Math.add({}, {})
    ** (FunctionClauseError) no function clause matching in Math.add/2

    iex> Math.add(%{}, %{})
    ** (FunctionClauseError) no function clause matching in Math.add/2
  """
  def add(value1, value2) do
  end

  @doc """
  Subtract two integers, strings, or lists.

  ## Examples

    iex> Math.subtract(10, 2)
    8
    iex> Math.subtract(20, 2)
    18

    iex> Math.subtract([1, 2], [1])
    [2]
    iex> Math.subtract([1, 2, 3, 4], [1, 3])
    [2, 4]

    iex> Math.subtract("abcd", "abc")
    "d"
    iex> Math.subtract("cbad", "abc")
    "d"
    iex> Math.subtract("abc", "xyz")
    "abc"
    iex> Math.subtract("abc", "xyza")
    "bc"

    iex> Math.subtract(1.0, 2.0)
    ** (FunctionClauseError) no function clause matching in Math.subtract/2

    iex> Math.subtract(2, "2")
    ** (FunctionClauseError) no function clause matching in Math.subtract/2

    iex> Math.subtract({}, {})
    ** (FunctionClauseError) no function clause matching in Math.subtract/2

    iex> Math.subtract(%{}, %{})
    ** (FunctionClauseError) no function clause matching in Math.subtract/2
  """
  def subtract(value1, value2) do
  end
end

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "math_with_guards_reading"
    "exercises" -> "math_with_guards_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b math-with-guards-exercise
$ git add .
$ git commit -m "finish math with guards exercise"
$ git push origin math-with-guards-exercise

Create a pull request from your math-with-guards-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

If you are interested in joining the next academy cohort, sign up here to receive more news when it is available.

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