Remove arithmetic koans

lib/koans/06_structs.ex

@@ -0,0 +1,58 @@
+defmodule Structs do
+  use Koans
+
+  defmodule Person do
+    defstruct [:name, :age ]
+  end
+
+  koan "Structs are defined and named after a module" do
+    person = %Person{}
+    assert person == :__
+  end
+
+  koan "You can access the fields of a struct" do
+    nobody = %Person{}
+    assert nobody.age == :__
+  end
+
+  koan "You can pass initial values to structs" do
+    joe = %Person{name: "Joe", age: 23}
+    assert joe.name == :__
+  end
+
+  koan "Update fields with the pipe '|' operator" do
+    joe = %Person{name: "Joe", age: 23}
+    older = %{ joe | age: joe.age + 10}
+    assert  older.age == :__
+  end
+
+  koan "The original struct is not affected by updates" do
+    joe = %Person{name: "Joe", age: 23}
+    assert %{ joe | age: joe.age + 10}.age == :__
+    assert joe.age == :__
+  end
+
+  koan "You can pattern match into the fields of a struct" do
+    %Person{age: age} = %Person{age: 22, name: "Silvia"}
+    assert age == :__
+  end
+
+  defmodule Plane do
+    defstruct passengers: 0, maker: :boeing
+  end
+
+  def plane?(%Plane{}), do: true
+  def plane?(_), do: false
+
+  koan "Or onto the type of the struct itself" do
+    assert plane?(%Plane{passengers: 417, maker: :boeing}) == :__
+    assert plane?(%Person{}) == :__
+  end
+
+
+  koan "Are basically maps" do
+    silvia = %Person{age: 22, name: "Silvia"}
+
+    assert Map.fetch!(silvia, :age) == :__
+  end
+end