Math With Guards

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

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Math With Guards

You’re going to create a Math module that uses guards 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 FunctionClauseError error if an invalid value is provided.

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

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

  def add(value1, value2) do
  end

  def subtract(value1, value2) do
  end
end

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 Math With Guards exercise"
$ git push

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