feat: ref

src/compile.rs

@@ -1,3 +1,5 @@
+use std::cell::OnceCell;
+
 use crate::bytecode::*;
 use crate::ir;
 use crate::ty::internal::Const;
@@ -19,7 +21,7 @@ pub fn compile(downgraded: ir::Downgraded) -> Program {
             .funcs
             .into_iter()
             .map(|func| Func {
-                env: None,
+                env: OnceCell::new(),
                 param: func.param.into(),
                 opcodes: Compiler::new().compile(*func.body),
             })