src/Pure/consts.ML

 and args_of_list (T :: Ts) i is = args_of T (i :: is) #> args_of_list Ts (i + 1) is
   | args_of_list [] _ _ = I;
 
 fun subscript (Type (_, Ts)) (i :: is) = subscript (nth Ts i) is
   | subscript T [] = T
-  | subscript T _ = raise Subscript;
+  | subscript _ _ = raise Subscript;
 
 in
 
 fun typargs_of T = map #2 (rev (args_of T [] []));