We cant build recursive enum type, as the size of that time would be infitite

src/lib.rs

@@ -1,2 +1,2 @@
-mod geometry;
+pub mod geometry;
 pub mod math;

src/main.rs

@@ -1,4 +1,10 @@
-use hello::math::Point3;
+use hello::geometry::Geometry;
+use hello::math::{Mat4x4, Point3};
+
+enum SceneGraphNode {
+    Geometry(Mat4x4, Geometry),
+    SubNode(Mat4x4, SceneGraphNode),
+}
 
 fn main() {
     let p1 = Point3::new(0.0, 0.0, 0.0);

src/math.rs

@@ -90,6 +90,10 @@ impl Sub for Point3 {
     }
 }
 
+pub struct Mat4x4 {
+    v: f64,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;