working on two levels

src/renderer/renderer.rs

@@ -120,6 +120,14 @@ mod tests {
         }
     }
 
+    impl<'a> Walkable for str {
+        type Output = str;
+
+        fn walk(&self, segment: &str) -> &str {
+            panic!("Tried to walk down a str");
+        }
+    }
+
     #[test]
     fn test_walk_path() {
         let context: HashMap<&str, &str> = [

src/renderer/walkable.rs

@@ -0,0 +1,7 @@
+use super::renderable::Renderable;
+
+pub trait Walkable {
+    type Output: ?Sized + Walkable;
+
+    fn walk(&self, segment: &str) -> &Self::Output;
+}