Add nominal role annotation for TaggedUnion

flipstone · Feb 23, 2024 · bc76b21 · bc76b21
1 parent 7302555
commit bc76b21
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/src/Shrubbery/TaggedUnion.hs b/src/Shrubbery/TaggedUnion.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE RoleAnnotations #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
@@ -40,6 +41,8 @@ import Shrubbery.Union (Union, dissectUnion)
 newtype TaggedUnion (taggedTypes :: [Tag])
   = TaggedUnion (Union (TaggedTypes taggedTypes))
 
+type role TaggedUnion nominal
+
 instance
   ( TaggedTypes taggedTypes ~ types
   , ShowBranches types