diff --git a/src/twopass.rs b/src/twopass.rs
index 66c1888..c30989a 100644
--- a/src/twopass.rs
+++ b/src/twopass.rs
@@ -112,6 +112,13 @@ struct BuildContext<'a> {
 }
 
 impl BuildContext<'_> {
+	fn new_toplevel() -> Self {
+		BuildContext {
+			parent: None,
+			scope: RefCell::new(Scope::new_toplevel()),
+		}
+	}
+
 	fn request(&self, name: &ast::Ident) -> Option<Ident> {
 		if let Some(ident) = self.scope.borrow().lookup(name) {
 			return Some(ident);
@@ -214,9 +221,5 @@ fn build_function(parent: &BuildContext<'_>, code: &ast::Function) -> Function {
 }
 
 pub fn build(code: &ast::Function) -> Function {
-	let mut root = BuildContext {
-		parent: None,
-		scope: RefCell::new(Scope::new_toplevel()),
-	};
-	build_function(&mut root, &code)
+	build_function(&BuildContext::new_toplevel(), &code)
 }