Test multiple koans together

lib/ast_mangler.ex

@@ -0,0 +1,25 @@
+defmodule ASTMangler do
+  def expand([], _), do: []
+  def expand({fun, context, args}, replacement) do
+    new_args = replace(args, replacement)
+    {fun, context, new_args}
+  end
+  def expand([do: thing], replacement) do
+    [do: expand(thing, replacement)]
+  end
+  def expand(n, _), do: n
+
+  def replace(args, b) do
+    args
+    |> Enum.find_index(fn(x) -> x == :__ end)
+    |> replace(args, b)
+  end
+
+  def replace(nil, ast, b) when is_list(ast) do
+    Enum.map(ast, fn(element) -> expand(element, b) end)
+  end
+
+  def replace(index, list, b) when is_integer(index) do
+    List.update_at(list, index, fn(_)-> b end)
+  end
+end

lib/runner.ex

@@ -41,7 +41,7 @@ defmodule Runner do
   end
 
   def test_single_koan(module, name, answer) do
-    case apply(module, name, []) do
+    case apply(module, name, [answer]) do
       :ok -> :passed
       error -> IO.inspect error
     end