ASTMangler supports multiple placeholders

lib/ast_mangler.ex

@@ -1,8 +1,25 @@
 defmodule ASTMangler do
+
+  def expand([do: remainder], replacements) when is_list(replacements) do
+    [do: expand(remainder, replacements)]
+  end
+  def expand(ast, replacements) when is_list(replacements) do
+    {node, _acc} = Macro.prewalk(ast, replacements, fn(node, acc) -> pre(node, acc) end)
+    node
+  end
   def expand(ast, replacement) do
-    Macro.prewalk(ast, fn(node) -> update(node, replacement) end)
+    expand(ast, [replacement])
   end
 
-  def update(:__, replacement), do: replacement
-  def update(node, _), do: node
+  def pre(:__, [first | remainder]), do: {first, remainder}
+  def pre(node, acc), do: {node, acc}
+
+
+  def count(ast) do
+    {_node, acc} = Macro.prewalk(ast, 0, fn(node, acc) -> count(node, acc) end)
+    acc
+  end
+
+  def count(:__, acc), do: {node, acc+1}
+  def count(node, acc), do: {node, acc}
 end

test/ast_mangler_test.exs

@@ -28,4 +28,22 @@ defmodule ASTManglerTest do
 
     assert [do: {:assert, [line: 5], [{:==, [line: 5], [true, true]}]}] == ASTMangler.expand(ast, true)
   end
+
+  test "multiple arguments" do
+    ast = [do: {:assert, [line: 5], [{:==, [line: 5], [:__, :__]}]}]
+
+    assert [do: {:assert, [line: 5], [{:==, [line: 5], [true, false]}]}] == ASTMangler.expand(ast, [true, false])
+  end
+
+  test "counts simple blanks" do
+    ast = quote do: 1 + :__
+
+    assert ASTMangler.count(ast) == 1
+  end
+
+  test "counts multiple blanks" do
+    ast = [do: {:assert, [line: 5], [{:==, [line: 5], [:__, :__]}]}]
+
+    assert ASTMangler.count(ast) == 2
+  end
 end