a small experiment on box

src/ast/ast.rs

@@ -26,6 +26,10 @@ fn check(t: Type) {
     }
 }
 
+// This requires unstable (nightly) feature
+// and won't compile using the stable toolchain
+//
+// Please use `check` instead for matching boxed values
 fn check2(t: Type) {
     use Type::*;
     match t {