diff --git a/content/blog/03_compiler_trees.md b/content/blog/03_compiler_trees.md
index 6e66af2..1e5e4ed 100644
--- a/content/blog/03_compiler_trees.md
+++ b/content/blog/03_compiler_trees.md
@@ -445,6 +445,7 @@ at the implementation now:
 
 {{< codeblock "C++" "compiler/03/ast.cpp" >}}
 
+{{< todo >}}Explain implementation, at least a little.{{< /todo >}}
 This looks good, but we're not done yet. We can type
 check expressions, but our program ins't
 made up of expressions. Rather, it's made up of