diff --git a/src/twopass.rs b/src/twopass.rs
index 24fa922..cb146be 100644
--- a/src/twopass.rs
+++ b/src/twopass.rs
@@ -2,6 +2,9 @@ use std::cell::RefCell;
 
 use crate::ast;
 
+#[derive(Debug, Clone)]
+pub struct OpenFunction(Function);
+
 #[derive(Debug, Clone)]
 pub struct Function {
 	name: Option<ast::Ident>,
@@ -234,6 +237,6 @@ fn build_function(parent: &BuildContext<'_>, code: &ast::Function) -> Function {
 	}
 }
 
-pub fn build(code: &ast::Function) -> Function {
-	build_function(&BuildContext::new_toplevel(), &code)
+pub fn build(code: &ast::Function) -> OpenFunction {
+	OpenFunction(build_function(&BuildContext::new_toplevel(), &code))
 }