diff --git a/src/vm/builtins.rs b/src/vm/builtins.rs
index b2839d4..4e4f8a5 100644
--- a/src/vm/builtins.rs
+++ b/src/vm/builtins.rs
@@ -144,6 +144,15 @@ impl MachineBuilder {
             }
         });
 
+        self.register_builtin_fun("S", |machine, _reentry| {
+            println!("- TOP");
+            for (i, obj) in machine.stack().iter().enumerate() {
+                println!("{}. {:?}", i, obj);
+            }
+            println!("- BOTTOM");
+            Ok(BuiltinExit::Return)
+        });
+
         /*
         //
         // ==