# Drills: Pattern Matching
```elixir
Mix.install([
{:jason, "~> 1.4"},
{:kino, "~> 0.9", override: true},
{:youtube, github: "brooklinjazz/youtube"},
{:hidden_cell, github: "brooklinjazz/hidden_cell"}
])
```
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## Drills: Pattern Matching
Drills help you develop familiarity and muscle memory with syntax through repeated exercises. Unlike usual problems, Drills are not intended to develop problem solving skills, they are purely for developing comfort and speed.
This set of drills is for [Pattern Matching](../reading/advanced_pattern_matching.livemd). Follow the instructions for each drill and complete them as quickly as you can.
## Treasure Matching
In this exercise, you're going to use **pattern matching** to extract the `"jewel"`
string from the data provided and bind it to a `jewel` variable. The first exercise is complete for example.
```elixir
[_, _, _, jewel] = [1, 2, 3, "jewel"]
jewel
```
Use pattern matching to bind a `jewel` variable to the `"jewel"` string. Each cell should return the `jewel` variable to prove it was bound correctly.
```elixir
[1, 2, 3, "jewel"]
```
```elixir
%{key1: "value", key2: "jewel"}
```
```elixir
%{1 => "jewel"}
```
```elixir
%{%{key: [1, 2, 3, 4, 5, {}]} => "jewel"}
```
```elixir
%{north: %{south: %{west: %{east: "jewel"}}}}
```
```elixir
[2, "jewel"]
```
```elixir
["jewel", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
```
```elixir
[1, "jewel", 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
```
```elixir
[1, 2, "jewel", 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
```
```elixir
[[], [1, [2, "jewel"]]]
```
```elixir
"here is the jewel"
```
```elixir
{"jewel"}
```
```elixir
{"jewel", 1}
```
```elixir
{1, 2, "jewel"}
```
```elixir
["jewel"] ++ Enum.to_list(1..100)
```
```elixir
[key: "jewel"]
```
```elixir
[south: "jewel", east: {1, 2}]
```
```elixir
Enum.map(1..4, fn each -> (each == 2 && "jewel") || each end)
```
```elixir
Enum.map(1..4, &((&1 > 3 && "jewel") || &1))
```
## Sum
Create a `Sum` module that uses **recursion** and **pattern matching** to sum all elements in a list. Avoid using the [Enum](https://hexdocs.pm/elixir/Enum.html) module or a comprehension.
<!-- livebook:{"force_markdown":true} -->
```elixir
iex> Sum.list([1, 2, 3])
6
```
<details style="background-color: lightgreen; padding: 1rem; border-radius: 0.5rem; margin: 1rem 0;">
<summary>Example Solution</summary>
```elixir
defmodule Sum do
def list(list, sum \\ 0)
def list([], sum), do: sum
def list([head | tail], sum), do: list(tail, sum + head)
end
```
</details>
```elixir
defmodule Sum do
@moduledoc """
iex> Sum.list([1, 2, 3])
6
"""
end
```
## Commit Your Progress
DockYard Academy now recommends you use the latest [Release](https://github.com/DockYard-Academy/curriculum/releases) 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 Drills: Pattern Matching exercise"
$ git push
```
We're proud to offer our open-source curriculum free of charge for anyone to learn from at their own pace.
We also offer a paid course where you can learn from an instructor alongside a cohort of your peers.
We will accept applications for the June-August 2023 cohort soon.
## Navigation
<div style="display: flex; align-items: center; width: 100%; justify-content: space-between; font-size: 1rem; color: #61758a; background-color: #f0f5f9; height: 4rem; padding: 0 1rem; border-radius: 1rem;">
<div style="display: flex;">
<i class="ri-home-fill"></i>
<a style="display: flex; color: #61758a; margin-left: 1rem;" href="../start.livemd">Home</a>
</div>
<div style="display: flex;">
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<a style="display: flex; color: #61758a; margin-left: 1rem;" href="https://github.com/DockYard-Academy/curriculum/issues/new?assignees=&labels=&template=issue.md&title=Drills: Pattern Matching">Report An Issue</a>
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<i class="ri-arrow-left-fill"></i>
<a style="display: flex; color: #61758a; margin-left: 1rem;" href="../reading/advanced_pattern_matching.livemd">Advanced Pattern Matching</a>
</div>
<div style="display: flex;">
<a style="display: flex; color: #61758a; margin-right: 1rem;" href="../exercises/drill-patternmatching-replace-nils.livemd">Replacing Nils</a>
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