with Ada.Text_IO;

procedure Main is
   type StringFunctor is access procedure(C: Character);
   procedure StringForeach (S: in String; F: in StringFunctor) is
   begin
      for i in S'Range loop
         F(S(i));
      end loop;
   end StringForeach;

   S: String := "Hello, world!";
begin
   StringForeach(S, Ada.Text_IO.Put'Access);
end Main;