Extract prefix constant for koans

lib/display.ex

@@ -39,6 +39,6 @@ defmodule Display do
   end
 
   defp display_koan(name) do
-    String.replace(to_string(name), "koan: ", "")
+    String.replace(to_string(name), Koans.prefix, "")
   end
 end

lib/koans.ex

@@ -1,6 +1,8 @@
 defmodule Koans do
+  @prefix "koan: "
+
   defmacro koan(name, body) do
-    compiled_name = :"koan: #{name}"
+    compiled_name = :"#{prefix}#{name}"
     quote do
       def unquote(compiled_name)() do
         try do
@@ -19,4 +21,8 @@ defmodule Koans do
       import ExUnit.Assertions
     end
   end
+
+  def prefix do
+    @prefix
+  end
 end

lib/runner.ex

@@ -50,6 +50,6 @@ defmodule Runner do
   end
 
   defp koan?(fun_name) do
-    String.starts_with?(to_string(fun_name), "koan: ")
+    String.starts_with?(to_string(fun_name), Koans.prefix)
   end
 end