import java.io.*;

class CharListDIO
{

 public static void print(CharList L)
 {
  System.out.print("[");
  if(!L.isempty())
     {
      System.out.print(L.head());
      printRestList(L.tail());
     }
  System.out.print("]");
 }

 private static void printRestList(CharList L)
 {
  if(!L.isempty())
     {
      System.out.print(","+L.head());
      printRestList(L.tail());
     }
 }

 public static CharList read(BufferedReader in) 
 throws IOException,ListFormatException
 {
  String excmess,line = in.readLine();
  try {
       if(line.charAt(0)!='[')
          {
           excmess="Expected '[', found '"+line.charAt(0)+"'";
           throw new ListFormatException(excmess);
          }
       else if(line.charAt(1)==']')
          return CharListD.empty();
       else 
          return readRestList(line,2).cons(line.charAt(1));
      }
  catch(StringIndexOutOfBoundsException e)
      {
       excmess="Unexpected end of line";
       throw new ListFormatException(excmess);
      }
 }

 private static CharList readRestList(String line,int i)
 throws ListFormatException
 {
  String excmess;
  if(line.charAt(i)==']')
     {
      if(++i!=line.length())
         {
          excmess="Extra characters: \"";
          excmess+=line.substring(i,line.length())+"\"";
          throw new ListFormatException(excmess);
         }
      return CharListD.empty();
     }
  else if(line.charAt(i)!=',')
     {
      excmess="Expected ']' or ','";
      excmess+=", found '"+line.charAt(i)+"'";
      throw new ListFormatException(excmess);
     }
  else
     return readRestList(line,i+2).cons(line.charAt(i+1));
 }
}