Add positional_count field to Lambda

This field is used for static optimization, determining if parameters
are purely positional.

src/ast/compiler/binder.rs

@@ -200,10 +200,30 @@ impl Binder {
                 
                 let compiled_fn = self.functions.pop().unwrap();
 
+                // 3. Static optimization: check if parameters are purely positional
+                let positional_count = match &params_bound.kind {
+                    BoundKind::Tuple { elements } => {
+                        let mut count = 0;
+                        let mut all_params = true;
+                        for e in elements {
+                            if matches!(e.kind, BoundKind::Parameter { .. }) {
+                                count += 1;
+                            } else {
+                                all_params = false;
+                                break;
+                            }
+                        }
+                        if all_params { Some(count) } else { None }
+                    }
+                    BoundKind::Parameter { .. } => Some(1),
+                    _ => None,
+                };
+
                 Ok(self.make_node(identity, BoundKind::Lambda {
-                    params: Box::new(params_bound),
+                    params: Rc::new(params_bound),
                     upvalues: compiled_fn.upvalues,
                     body: Rc::new(body_bound),
+                    positional_count,
                 }))
             },