Math With Protocols

Mix.install([
  {:jason, "~> 1.4"},
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  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
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Math With Protocols

You’re going to create a Math module that uses protocols to add or subtract integers, strings, and lists with the same add/2 and subtract/2 functions.

2 = Math.add(1, 1)
[1, 2, 3, 4] = Math.add([1, 2], [3, 4])
"hello there" = Math.add("hello there")

1 = Math.subtract(2, 1)
[2, 3] = Math.subtract([3, 2, 3], [3])
"ab" = Math.subtract("babc", "bc")

Raise a ProtocolUndefined error if an invalid value is provided.

Math.add(%{}, %{})
** (Protocol.UndefinedError) protocol Math not implemented for %{} of type Map

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

defprotocol Math do
  def add(value1, value2)
  def subtract(value1, value2)
end

defimpl Math, for: Integer do
  def add(integer1, integer2) do
    integer1 + integer2
  end

  def subtract(integer1, integer2) do
    integer1 - integer2
  end
end

defimpl Math, for: BitString do
  def add(string1, string2) do
    string1 <> string2
  end

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

defimpl Math, for: List do
  def add(list1, list2) do
    list1 ++ list2
  end

  def subtract(list1, list2) do
    list1 -- list2
  end
end

Define implementations for the Math protocol as documented below.

defprotocol Math do
  @moduledoc """
  iex> Math.add(1, 1)
  2
  iex> Math.add([1, 2], [3, 4])
  [1, 2, 3, 4]
  iex> Math.add("hello ", "there")
  "hello there" 

  iex> Math.subtract(2, 1)
  1
  iex> Math.subtract([3, 2, 3], [3])
  [2, 3] 
  iex> Math.subtract("babc", "bc")
  "ab"

  iex> Math.add({}, {})
  ** (Protocol.UndefinedError) protocol Math not implemented for {} of type Tuple
  """

  def add(value1, value2)

  def subtract(value1, value2)
end

# Define Implementations...

Commit Your Progress

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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 Math With Protocols exercise"
$ git push

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