Use bare double underscores instead of atoms

lib/koans/07_pattern_matching.ex

@@ -2,53 +2,53 @@ defmodule PatternMatching do
   use Koans
 
   koan "One matches one" do
-    assert match?(1, :__)
+    assert match?(1, __)
   end
 
   koan "A pattern can change" do
     a = 1
-    assert a = :__
+    assert a = __
   end
 
   koan "A pattern can also be strict" do
     a = 1
-    assert ^a = :__
+    assert ^a = __
   end
 
   koan "Patterns can be used to pull things apart" do
     [head | tail] = [1,2,3,4]
 
-    assert head == :__
-    assert tail == :__
+    assert head == __
+    assert tail == __
   end
 
   koan "And then put them back together" do
     head = 1
     tail = [2,3,4]
 
-    assert :__ == [head | tail]
+    assert __ == [head | tail]
   end
 
   koan "Some values can be ignored" do
     [_first, _second, third, _fourth] = [1,2,3,4]
 
-    assert third == :__
+    assert third == __
   end
 
   koan "Strings come apart just a easily" do
     "Shopping list: " <> items = "Shopping list: eggs, milk"
 
-    assert items == :__
+    assert items == __
   end
 
   koan "Patterns show what you really care about" do
     %{make: make} = %{type: "car", year: 2016, make: "Honda", color: "black"}
 
-    assert make == :__
+    assert make == __
   end
 
   koan "The pattern can make assertions about what it expects" do
-    assert match?([1, _second, _third], :__)
+    assert match?([1, _second, _third], __)
   end
 
   def make_noise(%{type: "cat"}), do: "Meow"
@@ -60,9 +60,9 @@ defmodule PatternMatching do
     cat = %{type: "cat", legs: 4, age: 3, color: "grey"}
     snake = %{type: "snake", legs: 0, age: 20, color: "black"}
 
-    assert make_noise(dog) == :__
-    assert make_noise(cat) == :__
-    assert make_noise(snake) == :__
+    assert make_noise(dog) == __
+    assert make_noise(cat) == __
+    assert make_noise(snake) == __
   end
 
   koan "Errors are shaped differently than sucessful results" do
@@ -71,6 +71,6 @@ defmodule PatternMatching do
       _ -> flunk("I should not happen")
     end
 
-    assert result == :__
+    assert result == __
   end
 end