src/Pure/Thy/thy_parse.ML

 (* mixfix annotations *)
 
 val infxl = "infixl" $$-- !! nat >> cat "Infixl";
 val infxr = "infixr" $$-- !! nat >> cat "Infixr";
 
-fun mk_binder ((name, x), y) =
-  let val (p1, p2) = if y = "None" then ("0", x) else (x, y);
-  in mk_triple (name, p1, p2) end;
-
-val binder = "binder" $$-- !! (string -- nat -- optional nat "None") 
-             >> (cat "Binder" o mk_binder);
+val binder = "binder" $$--
+  !! (string -- optional ("[" $$-- nat --$$ "]") "0" -- nat)
+  >> (cat "Binder" o mk_triple1);
 
 val opt_pris = optional ("[" $$-- !! (list nat --$$ "]")) [] >> mk_list;
 
 val mixfix = string -- !! (opt_pris -- optional nat "max_pri")
   >> (cat "Mixfix" o mk_triple2);