elixir-basics-workshop/index.html at master · toddthomas/elixir-basics-workshop · GitHub

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    <title>Elixir Basics Workshop</title>

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      <div class="slides">
        <section>
          <h1>Elixir Basics Workshop</h1>
          <p>Workshop given at <a href="http://www.meetup.com/boulder-elixir/">Boulder Elixir</a> on January 28th, 2016.</p>
        </section>

        <section>
          <h2>Preliminary Questions</h2>
          <ul>
            <li>Format: workshops, presentations, both?</li>
            <li>Timing: last Thursday of every month?</li>
          </ul>
        </section>

        <section>
          <h2>Why Elixir?</h2>
          <ul>
            <li>Really fast</li>
            <li>Easy to work with, even for big projects</li>
            <li>Fantastic tooling</li>
            <li>Concurrency!</li>
            <li>Auto-recover failures</li>
            <li>High up-time</li>
            <li>Hot code reloading</li>
            <li>Runs on BEAM (Erlang), 30 years battle tested</li>
          </ul>
        </section>

        <section>
          <h2>Workshop Goals</h2>
          <ul>
            <li>Learn basic syntax & how to work with Elixir</li>
            <li>Be able to solve simple problems</li>
            <li>Be exposed to Elixir's core features</li>
            <li>Be inspired to go home and learn more</li>
          </ul>
        </section>

        <section>
          <h2>Starting IEX</h2>
          <p>IEX is Elixir's interactive shell. Ships with Elixir.</p>
          <p>In the console, run <code>iex</code>.</p>
          <pre><code>
$ iex
Erlang/OTP 17 [erts-6.4] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]
Interactive Elixir (1.0.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)>
          </code></pre>
          <p>To quit, press Ctrl + C twice.</p>
        </section>

        <section>
          <h2>Assigning Variables</h2>
          <pre><code>
iex> x = 2
2

iex> y = 3
3

# {...} are tuples
iex> {x, y} = {2, 3}
{2, 3}

iex> {a, b, c} = {4, 5, 6}
{4, 5, 6}
          </code></pre>
          <p>Mostly similar to other languages</p>
        </section>

        <section>
          <h2>Pattern Matching</h2>
          <pre><code>
iex> {:ok, val} = {:ok, 42}
{:ok, 42}

iex> val
42

iex> {:ok, val} = {:error, nil}
** (MatchError) no match of right hand side value: {:error, nil}
          </code></pre>
          <p>You don't actually assign variables, you pattern match them.</p>
          <p>Variables get assigned if the pattern matches.</p>
          <p>Equal sign works like how it does in math.</p>
        </section>

        <section>
          <h2>Exercise</h2>
          <ol>
            <li>Load <code>iex</code></li>
            <li>Assign <code>42</code> to a single variable</li>
            <li>Assign values to the tuple <code>{:ok, value, message}</code> that pattern match</li>
            <li>Try to assign values to the tuple <code>{:ok, value, message}</code> that DON'T pattern match</li>
          </ol>
          <p>-</p>
          <p>Take 5 minutes. Josh and I will be walking around. If you have a question, raise your hand.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
iex> value = 42
42

iex> {:ok, value, message} = {:ok, 5, "Hey there!"}
{:ok, 5, "Hey there!"}

iex> {:ok, value, message} = {:error, nil, "Nope!"}
** (MatchError) no match of right hand side value: {:error, nil, "Nope!"}
          </code></pre>
        </section>

        <section>
          <h2>If Statements</h2>
          <pre><code>
iex> if true do
...>   "Hello!"
...> else
...>   "Goodbye!"
...> end
"Hello!"
          </code></pre>
          <p>Similar to what you're used to</p>
          <p>Don't forget the <code>do</code>!</p>
        </section>

        <section>
          <h2>Case Statements</h2>
          <pre><code>
iex> case true do
...>   true -> "Hello!"
...>   _ -> "This will match anything except true"
...> end
"Hello!"
          </code></pre>
          <p>You will probably use <code>case</code> and pattern matching more than <code>if</code></p>
        </section>

        <section>
          <h2>Case Statements With Pattern Matching</h2>
          <pre><code>
iex> case {:ok, 42} do
...>   {:ok, 42} -> "The number is 42!"
...>   {:ok, val} -> "The number is not 42. It is: #{val}"
...>   _ -> "Matches everything else."
...> end
"The number is 42!"
          </code></pre>
        </section>

        <section>
          <h2>Exercise</h2>
          <ol>
            <li>Write a <code>case</code> statement that handles the tuples <code>{:ok, 42}</code> and <code>{:error, nil}</code>.</li>
            <li>Add a catch-all condition (underscore)</li>
          </ol>
          <p>-</p>
          <p>Take 10 minutes. Josh and I will be walking around.</p>
          <p>If you have a question, raise your hand or ask your neighbor.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
iex> case {:ok, 42} do
...>   {:ok, value} -> value
...>   {:error, _} -> "Error!"
...>   _ -> "I'm not sure what to do..."
...> end
42
          </code></pre>
        </section>

        <section>
          <h2>Lists</h2>
          <p>Known as Arrays in other languages.</p>
          <p>Can contain multiple types.</p>
          <p>Can concatenate with <code>++</code>.</p>

          <pre><code>
iex> a = [1, 2, 3, 4]
[1, 2, 3, 4]

iex> b = [1, "a", true, 4]
[1, "a", true, 4]

iex> c = a ++ b
[1, 2, 3, 4, 1, "a", true, 4]
          </code></pre>
        </section>

        <section>
          <h2>The Enum Package</h2>
          <p>Enum has lots of functions to manipulate Enumerables.</p>
          <p>All of your favorite functions: map, reduce, sort, shuffle, etc.</p>

          <pre><code>
iex> Enum.max([1, 3, 2])
3

iex> Enum.sort([3, 2, 4, 7, 1, 9])
[1, 2, 3, 4, 7, 9]

iex> Enum.shuffle([1, 2, 3, 4])
[4, 3, 1, 2]
          </code></pre>

          <p><a href="http://elixir-lang.org/docs/stable/elixir/Enum.html">Link to docs</a></p>
        </section>

        <section>
          <h2>Enum cont.</h2>
          <p>Many Enum functions take a function as an argument.</p>
          <p>Map, for instance:</p>
          <p><code>Enum.map(enumerable, function)</code></p>

          <pre><code>
iex(13)> Enum.map([1, 2, 3], fn x -> x + 1 end)
[2, 3, 4]
          </code></pre>
        </section>

        <section>
          <h2>Detour: Anonymous Functions</h2>
          <p>Use <code>fn (args) -></code> and <code>end</code> to define.</p>
          <pre><code>
iex> add = fn (a, b) -> a + b end
#Function<12.90072148/2 in :erl_eval.expr/5>

iex> add.(1, 2)
3
          </code></pre>
          <p>Note you have to use <code>.</code> to invoke the function</p>
          <p>Most often used when passing as an argument</p>
        </section>

        <section>
          <h2>Let's see that Enum again</h2>
          <pre><code>
iex(13)> Enum.map([1, 2, 3], fn x -> x + 1 end)
[2, 3, 4]
          </code></pre>
          <p>Passing in an anonymous function that Enum calls</p>
        </section>

        <section>
          <h2>Pipe Character</h2>
          <p>Similar to Unix pipe</p>
          <p>Takes output of first function and passes as first argument to next function</p>
          <pre><code>
iex(13)> Enum.map([1, 2, 3], fn x -> x + 1 end) |> Enum.take(1)
[2]

# equivalent to
list = Enum.map([1, 2, 3], fn x -> x + 1 end)
Enum.take(list, 1)
          </code></pre>
        </section>

        <section>
          <h2>Exercise</h2>
          <ol>
            <li>Combine two lists</li>
            <li>Use <code>Enum.map</code> to square this list of numbers: <code>[1, 2, 3, 4]</code></li>
            <li>Using the code from #2 and the pipe character, square a list of numbers and then shuffle them using <code>Enum.shuffle()</code></li>
          </ol>
          <p>-</p>
          <p>Take 5 minutes. Josh and I will be walking around.</p>
          <p>If you have a question, raise your hand or ask your neighbor.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
iex> [1, 2, 3] ++ [3, 4, 5]
[1, 2, 3, 3, 4, 5]

iex> Enum.map([1, 2, 3, 4], fn x -> x * x end)
[1, 4, 9, 16]

iex> Enum.map([1, 2, 3, 4], fn x -> x * x end) |> Enum.shuffle
[4, 16, 1, 9]
          </code></pre>
        </section>

        <section>
          <h2>Maps</h2>
          <p><code>%{key: value, key: value}</code></p>
          <pre><code>
iex> a = %{a: 13, b: true, c: "cat"}
%{a: 13, b: true, c: "cat"}

iex> a.a
13

iex> a.c
"cat"

iex> a[:c]
"cat"

iex> Map.put(a, :d, "hey there") # Map.put(map, key, value)
%{a: 13, b: true, c: "cat", d: "hey there"}
          </code></pre>
        </section>

        <section>
          <h2>Enum With Maps</h2>
          <p>Pass in the map and a function</p>
          <pre><code>
iex> my_map = %{a: 1, b: 2, c: 3}
%{a: 1, b: 2, c: 3}

iex> Enum.map(my_map, fn {key, val} -> val * val end)
[1, 4, 9]

iex> Enum.map(my_map, fn {key, val} -> val * val end) |> Enum.max
9

iex> Enum.filter(my_map, fn {key, val} -> val == 2 end)
[b: 2]
          </code></pre>
        </section>

        <section>
          <h2>Exercise</h2>
          <ol>
            <li>Given the map <code>%{a: 1, b: 2}</code>, add the element <code>c: 3</code>. Hint: Use <code>Map.put(enum, key, value)</code></li>
            <li>Use <code>Enum.filter(enum, function)</code> to get all items in <code>%{a: 3, b: 12, c: 9, d: 15}</code> where value is greater than 10. </li>
            <li>Using pipes and <code>Enum.take(enum, number)</code>, modify code in #1 to only return 1 item.</li>
          </ol>
          <p>Hint: Use <code>{key, value}</code> to extract the keys and values in your anonymous function</p>
          <p>-</p>
          <p>Take 10 minutes. Josh and I will be walking around.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
iex> map = %{a: 3, b: 12, c: 9, d: 15}
%{a: 3, b: 12, c: 9, d: 15}

iex> Enum.filter(map, fn {key, val} -> val > 10 end)
[b: 12, d: 15]

iex> Enum.filter(map, fn {key, val} -> val > 10 end) |> Enum.take(1)
[b: 12]
          </code></pre>
        </section>

        <section>
          <h2>Modules</h2>
          <p>Let's put our code into files!</p>
          <pre><code>
# lib/workshop.exs
defmodule Workshop do

  def add(a, b) do
    a + b
  end

end
          </code></pre>
        </section>

        <section>
          <h2>Running Modules In iex</h2>
          <p>You have to tell iex to compile the file</p>
          <p>Compiles into Erlang bytecode</p>
          <pre><code>
$ iex lib/workshop.exs
...
iex> Workshop.add(1, 2)
3

# can also compile from within iex
iex> c "lib/workshop.exs"
[Workshop]
          </code></pre>
        </section>

        <section>
          <h2>Private Functions</h2>
          <p>Can only be called from its module</p>
          <p>Cannot be unit tested</p>
          <pre><code>
# lib/workshop.exs
defmodule Workshop do
  ...

  defp log_value(val) do
    IO.puts "Value is: #{val}"
  end

end
          </code></pre>
        </section>

        <section>
          <h2>Exercise</h2>
          <ol>
            <li>Add a <code>sum</code> function that sums every number in a list</li>
            <li>Uncomment the tests for <code>sum</code> in <code>test/workshop_test.exs</code> and make them pass</li>
          </ol>
          <p>Hint: use <code>Enum.reduce(enum, 0, fn (num, accumulator))</code></p>
          <p>Run tests with <code>mix test</code> in console.</p>
          <p>-</p>
          <p>Take 10 minutes. Josh and I will be walking around.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
def sum(list) do
  Enum.reduce(list, 0, fn (num, acc) -> num + acc end)
end
          </code></pre>
        </section>

        <section>
          <h3>Pattern Matching With Functions</h3>
          <p>Function signatures can use pattern matching too!</p>
          <pre><code>
# lib/workshop.exs
defmodule Workshop do
  ...

  def divide(_, 0) do
    "You can't divide by zero!"
  end

  def divide(dividend, divisor) do
    dividend / divisor
  end

end
          </code></pre>
          <p>Multiple functions will get called based on what matches</p>
        </section>

        <section>
          <h2>Exercise</h2>
          <p>Let's write a variation of FizzBuzz!</p>
          <ol>
            <li>Write multiple versions of the function <code>fizzbuzz</code></li>
            <li>If called with <code>3</code>, return <code>"Fizz"</code></li>
            <li>If called with <code>5</code>, return <code>"Buzz"</code></li>
            <li>If called with anything else, simply return what was passed in</li>
          </ol>
          <p>Uncomment and run tests with <code>mix test</code>.</p>
          <p>-</p>
          <p>Take 10 minutes. Josh and I will be walking around.</p>
          <p>If you have a question, raise your hand or ask your neighbor.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
def fizzbuzz(3) do
  "Fizz"
end

def fizzbuzz(5) do
  "Buzz"
end

def fizzbuzz(val) do
  val
end
          </code></pre>
        </section>

        <section>
          <h3>Recursion</h3>
          <p>Basic definition: when a function calls itself</p>
          <p>Because Elixir is a functional language, recursion is used in place of loops</p>
          <p>Functions in Enum are implemented using recursion</p>
        </section>

        <section>
          <h3>Lists</h3>
          <p>All lists are linked lists</p>
          <p>Every list can be separated into the first element and the rest of the list</p>
          <pre><code>
iex> [head | tail] = [1, 2, 3, 4]
[1, 2, 3, 4]

iex> head
1

iex> tail
[2, 3, 4]
          </code></pre>
        </section>

        <section>
          <h3>Lists</h3>
          <p>Last element of every list is an empty list</p>
          <pre><code>
iex> [head | tail] = [1]
[1]

iex> head
1

iex> tail
[]
          </code></pre>
        </section>

        <section>
          <h3>Recursion With Lists</h3>
          <p>We can define recursive functions using pattern matching and using multiple functions</p>
          <pre><code>
def thing([]) do
  []
end

def thing([head | tail]) do
  ...
end
          </code></pre>
          <p>Because last element is always empty list, that is our base case</p>
          <p>After that, we can define functions that do the work</p>
        </section>

        <section>
          <h3>Recursion With Lists - Example</h3>
          <p>Let's add 1 to every number in a list</p>
          <pre><code>
def add_one([]) do
  []
end
          </code></pre>
          <p>Define base case</p>
        </section>

        <section>
          <h3>Recursion With Lists - Example</h3>
          <p>Let's add 1 to every number in a list</p>
          <pre><code>
def add_one([]) do
  []
end

def add_one([head | tail]) do
  # todo
end
          </code></pre>
          <p>Define second function and assign first element <code>head</code> and rest of list <code>tail</code></p>
        </section>

        <section>
          <h3>Recursion With Lists - Example</h3>
          <p>Let's add 1 to every number in a list</p>
          <pre><code>
def add_one([]) do
  []
end

def add_one([head | tail]) do
  [head + 1 | ...]
end
          </code></pre>
          <p>In second function, declare new list with <code>head + 1</code> as the first element</li>
        </section>

        <section>
          <h3>Recursion With Lists - Example</h3>
          <p>Let's add 1 to every number in a list</p>
          <pre><code>
def add_one([]) do
  []
end

def add_one([head | tail]) do
  [head + 1 | add_one(tail)]
end
          </code></pre>
          <p>Recursively fill in the rest of the elements (call <code>add_one</code>)</p>
          <p>When no more elements, the first function matches, and the stack returns</p>
        </section>

        <section>
          <h2>In iex</h2>
          <pre><code>
iex> Workshop.add_one([])
[]

iex> Workshop.add_one([1])
[2]

iex> Workshop.add_one([1, 2, 3])
[2, 3, 4]

iex> Workshop.add_one([1, 2, 3, 10])
[2, 3, 4, 11]
          </code></pre>
        </section>

        <section>
          <h2>Exercise</h2>
          <p>Using recursion and pattern matching, write the function <code>square_list</code> which squares a list of numbers</p>
          <ol>
            <li>Define your base case (handle empty list)</li>
            <li>Define second function that assigns <code>head</code> and <code>tail</code></li>
            <li>Return a new list with the first element being the squared <code>head</code></li>
            <li>Recursively fill in the rest of the list by calling <code>square_list</code></li>
          </ol>
          <p>Uncomment and run tests with <code>mix test</code>.</p>
        </section>

        <section>
          <h2>Exercise Answer</h2>
          <pre><code>
def square_list([]) do
  []
end

def square_list([head | tail]) do
  [head * head | square_list(tail)]
end
          </code></pre>
        </section>

        <section>
          <h2>Discussion</h2>
          <p>Too hard?</p>
          <p>Too easy?</p>
          <p>Other thoughts?</p>
        </section>

        <section>
          <h2>Next Time</h2>
          <p>Presentations: message me if you want to talk</p>
        </section>
      </div>
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