better structure

src/lib.rs

@@ -3,8 +3,13 @@ use std::fmt::Debug;
 pub mod components;
 pub mod macros;
 
-pub trait Component: Debug {}
+pub trait Component: Debug {
+    fn render(&mut self) -> String {
+        String::new()
+    }
+}
 
 pub struct ComponentParams {
     pub children: Vec<Box<dyn Component>>,
+    pub expr: String,
 }