src/Tools/Code/code_haskell.ML

               :: print_co co
               :: map ((fn p => Pretty.block [str "| ", p]) o print_co) cos
               @ (if deriving_show name then [str "deriving (Read, Show)"] else [])
             )
           end
-      | print_stmt (name, Code_Thingol.Class (_, (v, (super_classes, classparams)))) =
+      | print_stmt (name, Code_Thingol.Class (_, (v, ((super_classes, _), classparams)))) =
           let
             val tyvars = intro_vars [v] reserved;
             fun print_classparam (classparam, ty) =
               semicolon [
                 (str o deresolve_base) classparam,