class CharListF implements CharList
{
// A very inefficient implementation of CharList

 private InnerList content;
 public static final int MAX=100;

 private CharListF(InnerList L)
 {
  content=L;
 }

 public char head()
 {
  return content.array[content.size-1];
 }

 public CharList tail()
 {
  InnerList L = new InnerList(content.size-1,content.array);
  return new CharListF(L);
 }

 public CharList cons(char ch)
 {
  char[] a = (char[]) content.array.clone();
  a[content.size]=ch;
  InnerList L = new InnerList(content.size+1,a);
  return new CharListF(L);
 }

 public static CharList empty()
 {
  InnerList L = new InnerList(0,new char[MAX]);
  return new CharListF(L);
 }

 public boolean isempty()
 {
  return (content.size==0);
 }

 private static class InnerList
 {
  int size;
  char[] array;
 
  InnerList(int n,char[] a)
  {
   size=n;
   array=a;
  }
 }
}