Add credo to the project and:

- Run mix credo --all to identify possible code optimizations
 - Resolve most of the errors generated by credo such as:
   - Numbers larger than 9999 should be written with underscores: 58_127
   - Modules should have a @moduledoc tag
   - Comparison will always return true

lib/blanks.ex

@@ -1,4 +1,5 @@
 defmodule Blanks do
+  @moduledoc false
   def replace(ast, replacements) do
     replacements = List.wrap(replacements)
 

lib/display.ex

@@ -1,4 +1,5 @@
 defmodule Display do
+  @moduledoc false
   use GenServer
 
   alias IO.ANSI
@@ -20,7 +21,7 @@ defmodule Display do
     {:noreply, %{state | clear_screen: false}}
   end
 
-  def handle_cast(:clear_screen, state = %{clear_screen: true}) do
+  def handle_cast(:clear_screen, %{clear_screen: true} = state) do
     IO.puts(ANSI.clear())
     IO.puts(ANSI.home())
 

lib/display/colours.ex

@@ -1,4 +1,5 @@
 defmodule Display.Paint do
+  @moduledoc false
   def red(str), do: painter().red(str)
   def cyan(str), do: painter().cyan(str)
   def green(str), do: painter().green(str)
@@ -13,6 +14,7 @@ defmodule Display.Paint do
 end
 
 defmodule Display.Colours do
+  @moduledoc false
   alias IO.ANSI
 
   def red(str), do: colourize(ANSI.red(), str)
@@ -26,6 +28,7 @@ defmodule Display.Colours do
 end
 
 defmodule Display.Uncoloured do
+  @moduledoc false
   def red(str), do: str
   def cyan(str), do: str
   def green(str), do: str

lib/display/failure.ex

@@ -1,4 +1,5 @@
 defmodule Display.Failure do
+  @moduledoc false
   alias Display.Paint
 
   @no_value :ex_unit_no_meaningful_value

lib/display/intro.ex

@@ -1,11 +1,12 @@
 defmodule Display.Intro do
+  @moduledoc false
   alias Display.Paint
 
   def intro(module, modules) do
-    if not (module in modules) do
-      show_intro(module.intro)
-    else
+    if module in modules do
       ""
+    else
+      show_intro(module.intro)
     end
   end
 

lib/display/notification.ex

@@ -1,4 +1,5 @@
 defmodule Display.Notifications do
+  @moduledoc false
   alias Display.Paint
 
   def congratulate do
@@ -13,8 +14,7 @@ defmodule Display.Notifications do
   defp module_names(modules) do
     modules
     |> Enum.map(&Atom.to_string/1)
-    |> Enum.map(&name/1)
-    |> Enum.join(", ")
+    |> Enum.map_join(", ", &name/1)
     |> Paint.red()
   end
 

lib/display/progress_bar.ex

@@ -1,4 +1,5 @@
 defmodule Display.ProgressBar do
+  @moduledoc false
   @progress_bar_length 30
 
   def progress_bar(%{current: current, total: total}) do

lib/elixir_koans.ex

@@ -1,4 +1,5 @@
 defmodule ElixirKoans do
+  @moduledoc false
   use Application
 
   def start(_type, _args) do

lib/execute.ex

@@ -1,4 +1,5 @@
 defmodule Execute do
+  @moduledoc false
   def run_module(module, callback \\ fn _result, _module, _koan -> nil end) do
     Enum.reduce_while(module.all_koans, :passed, fn koan, _ ->
       module

lib/koans.ex

@@ -1,4 +1,5 @@
 defmodule Koans do
+  @moduledoc false
   defp valid_name(name) do
     Regex.match?(~r/([A-Z]|\.\.\.).+/, name)
   end

lib/koans/01_equalities.ex

@@ -1,4 +1,5 @@
 defmodule Equalities do
+  @moduledoc false
   use Koans
 
   @intro """

lib/koans/02_strings.ex

@@ -1,4 +1,5 @@
 defmodule Strings do
+  @moduledoc false
   use Koans
 
   @intro "Strings"

lib/koans/03_numbers.ex

@@ -1,4 +1,5 @@
 defmodule Numbers do
+  @moduledoc false
   require Integer
   use Koans
 
@@ -49,7 +50,7 @@ defmodule Numbers do
   end
 
   koan "Let's grab the individual digits in a list" do
-    individual_digits = Integer.digits(58127)
+    individual_digits = Integer.digits(58_127)
     assert individual_digits == ___
   end
 

lib/koans/04_atoms.ex

@@ -1,4 +1,5 @@
 defmodule Atoms do
+  @moduledoc false
   use Koans
 
   @intro "Atoms"

lib/koans/05_tuples.ex

@@ -1,4 +1,5 @@
 defmodule Tuples do
+  @moduledoc false
   use Koans
 
   @intro "Tuples"

lib/koans/06_lists.ex

@@ -1,4 +1,5 @@
 defmodule Lists do
+  @moduledoc false
   use Koans
 
   @intro "Lists"

lib/koans/07_keyword_lists.ex

@@ -1,4 +1,5 @@
 defmodule KeywordLists do
+  @moduledoc false
   use Koans
 
   @intro "KeywordLists"

lib/koans/08_maps.ex

@@ -1,4 +1,5 @@
 defmodule Maps do
+  @moduledoc false
   use Koans
 
   @intro "Maps"

lib/koans/09_map_sets.ex

@@ -1,4 +1,5 @@
 defmodule MapSets do
+  @moduledoc false
   use Koans
 
   @intro "My name is Set, MapSet."

lib/koans/10_structs.ex

@@ -1,9 +1,11 @@
 defmodule Structs do
+  @moduledoc false
   use Koans
 
   @intro "Structs"
 
   defmodule Person do
+    @moduledoc false
     defstruct [:name, :age]
   end
 
@@ -35,10 +37,12 @@ defmodule Structs do
   end
 
   defmodule Plane do
+    @moduledoc false
     defstruct passengers: 0, maker: :boeing
   end
 
   defmodule Airline do
+    @moduledoc false
     defstruct plane: %Plane{}, name: "Southwest"
   end
 

lib/koans/11_sigils.ex

@@ -1,4 +1,5 @@
 defmodule Sigils do
+  @moduledoc false
   use Koans
 
   @intro "Sigils"

lib/koans/12_pattern_matching.ex

@@ -1,4 +1,5 @@
 defmodule PatternMatching do
+  @moduledoc false
   use Koans
 
   @intro "PatternMatching"
@@ -94,6 +95,7 @@ defmodule PatternMatching do
   end
 
   defmodule Animal do
+    @moduledoc false
     defstruct [:kind, :name]
   end
 
@@ -103,6 +105,7 @@ defmodule PatternMatching do
   end
 
   defmodule Plane do
+    @moduledoc false
     defstruct passengers: 0, maker: :boeing
   end
 

lib/koans/13_functions.ex

@@ -1,4 +1,5 @@
 defmodule Functions do
+  @moduledoc false
   use Koans
 
   @intro "Functions"
@@ -104,8 +105,7 @@ defmodule Functions do
     result =
       "full-name"
       |> String.split("-")
-      |> Enum.map(&String.capitalize/1)
-      |> Enum.join(" ")
+      |> Enum.map_join(" ", &String.capitalize/1)
 
     assert result == ___
   end

lib/koans/14_enums.ex

@@ -1,4 +1,5 @@
 defmodule Enums do
+  @moduledoc false
   use Koans
 
   @intro "Enums"

lib/koans/15_processes.ex

@@ -1,4 +1,5 @@
 defmodule Processes do
+  @moduledoc false
   use Koans
 
   @intro "Processes"
@@ -88,8 +89,12 @@ defmodule Processes do
 
     send(pid, {:hello, self()})
 
-    timeout = 100 # ms
-    failure_message = "Sorry, I didn't get the right message. Look at the message that is sent back very closely, and try again"
+    # ms
+    timeout = 100
+
+    failure_message =
+      "Sorry, I didn't get the right message. Look at the message that is sent back very closely, and try again"
+
     assert_receive ___, timeout, failure_message
   end
 

lib/koans/16_tasks.ex

@@ -1,4 +1,5 @@
 defmodule Tasks do
+  @moduledoc false
   use Koans
 
   @intro "Tasks"

lib/koans/17_agents.ex

@@ -1,4 +1,5 @@
 defmodule Agents do
+  @moduledoc false
   use Koans
 
   @intro "Agents"

lib/koans/18_genservers.ex

@@ -1,9 +1,11 @@
 defmodule GenServers do
+  @moduledoc false
   use Koans
 
   @intro "GenServers"
 
   defmodule Laptop do
+    @moduledoc false
     use GenServer
 
     #####

lib/koans/19_protocols.ex

@@ -1,4 +1,5 @@
 defmodule Protocols do
+  @moduledoc false
   use Koans
 
   @intro "Want to follow the rules? Adhere to the protocol!"
@@ -12,13 +13,25 @@ defmodule Protocols do
   end
 
   defmodule Painter do
+    @moduledoc false
     @derive Artist
     defstruct name: ""
   end
 
-  defmodule(Musician, do: defstruct(name: "", instrument: ""))
-  defmodule(Dancer, do: defstruct(name: "", dance_style: ""))
-  defmodule(Physicist, do: defstruct(name: ""))
+  defmodule Musician do
+    @moduledoc false
+    defstruct(name: "", instrument: "")
+  end
+
+  defmodule Dancer do
+    @moduledoc false
+    defstruct(name: "", dance_style: "")
+  end
+
+  defmodule Physicist do
+    @moduledoc false
+    defstruct(name: "")
+  end
 
   defimpl Artist, for: Musician do
     def perform(musician) do

lib/koans/20_comprehensions.ex

@@ -1,32 +1,32 @@
 defmodule Comprehensions do
+  @moduledoc false
   use Koans
 
   @intro "A comprehension is made of three parts: generators, filters, and collectibles. We will look at how these interact with each other"
 
   koan "The generator, `n <- [1, 2, 3, 4]`, is providing the values for our comprehension" do
-    assert (for n <- [1, 2, 3, 4], do: n * n) == ___
+    assert for(n <- [1, 2, 3, 4], do: n * n) == ___
   end
 
   koan "Any enumerable can be a generator" do
-    assert (for n <- 1..4, do: n * n) == ___
+    assert for(n <- 1..4, do: n * n) == ___
   end
 
   koan "A generator specifies how to extract values from a collection" do
-    collection = [["Hello","World"], ["Apple", "Pie"]]
-    assert (for [a, b] <- collection, do: "#{a} #{b}") == ___
+    collection = [["Hello", "World"], ["Apple", "Pie"]]
+    assert for([a, b] <- collection, do: "#{a} #{b}") == ___
   end
 
   koan "You can use multiple generators at once" do
-    assert (for x <- ["little", "big"], y <- ["dogs", "cats"], do: "#{x} #{y}") == ___
+    assert for(x <- ["little", "big"], y <- ["dogs", "cats"], do: "#{x} #{y}") == ___
   end
 
   koan "Use a filter to reduce your work" do
-    assert (for n <- [1, 2, 3, 4, 5, 6], n > 3, do: n) == ___
+    assert for(n <- [1, 2, 3, 4, 5, 6], n > 3, do: n) == ___
   end
 
   koan "Add the result of a comprehension to an existing collection" do
     collection = for x <- ["Pecan", "Pumpkin"], into: %{}, do: {x, "#{x} Pie"}
     assert collection == ___
   end
-
 end

lib/meditate.ex

@@ -1,4 +1,5 @@
 defmodule Mix.Tasks.Meditate do
+  @moduledoc false
   use Mix.Task
 
   @shortdoc "Start the koans"

lib/runner.ex

@@ -1,4 +1,5 @@
 defmodule Runner do
+  @moduledoc false
   use GenServer
 
   def koan?(koan) do

lib/tracker.ex

@@ -1,4 +1,5 @@
 defmodule Tracker do
+  @moduledoc false
   alias __MODULE__
 
   defstruct total: 0,

lib/watcher.ex

@@ -1,4 +1,5 @@
 defmodule Watcher do
+  @moduledoc false
   use GenServer
 
   def start_link() do