import java.io.*;

class UseCharListsD1
{

 public static void main(String[] args) throws IOException
 {
  BufferedReader in = new BufferedReader(
                        new InputStreamReader(System.in));
  CharList L1=null,L2=null,L3;
  char ch1,ch2;
  try {
       System.out.print("Enter first list of characters: ");
       L1 = CharListDIO.read(in);
       System.out.print("Enter second list of characters: ");
       L2 = CharListDIO.read(in);
      }
  catch(ListFormatException e)
      {
       System.out.println("Error: "+e.getMessage());
      }
  System.out.print("The lists are: ");
  CharListDIO.print(L1);
  System.out.print(" and ");
  CharListDIO.print(L2);
  System.out.println();
  System.out.println("Call append ");
  L3=append(L1,L2);
  System.out.print("The lists are now: ");
  CharListDIO.print(L1);
  System.out.print(" and ");
  CharListDIO.print(L2);
  System.out.print(" and ");
  CharListDIO.print(L3);
  System.out.println();
  System.out.print("Enter first character: ");
  ch1=in.readLine().charAt(0);
  System.out.print("Enter second character: ");
  ch2=in.readLine().charAt(0);
  System.out.print("Call change of first to ");
  System.out.println("second character in second list ");
  L3=change(ch1,ch2,L2);
  System.out.print("The lists are now: ");
  CharListDIO.print(L1);
  System.out.print(" and ");
  CharListDIO.print(L2);
  System.out.print(" and ");
  CharListDIO.print(L3);
  System.out.println();
 }

 public static CharList append(CharList L1,CharList L2)
 {
  if(L1.isempty())
     return L2;
  else
     {
      CharList L3 = append(L1.tail(),L2);
      return L3.cons(L1.head());
     }
 }

 public static CharList change(char ch1,char ch2,CharList L)
 {
  if(L.isempty())
     return CharListD.empty();
  else 
     {
      CharList T=change(ch1,ch2,L.tail());
      char h=L.head();
      if(h==ch1)
         return T.cons(ch2);
      else
         return T.cons(h);
     }
 }

}