code: package jfkbits;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.Reader;
  import java.io.StreamTokenizer;
  import java.io.StringReader;
  import java.util.Iterator;
  
  public class LispTokenizer implements Iterator<Token>
  {
      // Instance variables have default access to allow unit tests access.
      StreamTokenizer m_tokenizer;
      IOException m_ioexn;
  
      /** Constructs a tokenizer that scans input from the given string.
       * @param src A string containing S-expressions.
       */
      public LispTokenizer(String src)
      {
          this(new StringReader(src));
      }
  
      /** Constructs a tokenizer that scans input from the given Reader.
       * @param r Reader for the character input source
       */
      public LispTokenizer(Reader r)
      {
          if(r == null)
              r = new StringReader("");
          BufferedReader buffrdr = new BufferedReader(r);
          m_tokenizer = new StreamTokenizer(buffrdr);
          m_tokenizer.resetSyntax(); // We don't like the default settings
  
          m_tokenizer.whitespaceChars(0, ' ');
          m_tokenizer.wordChars(' '+1,255);
          m_tokenizer.ordinaryChar('(');
          m_tokenizer.ordinaryChar(')');
          m_tokenizer.ordinaryChar('\'');
          m_tokenizer.commentChar(';');
          m_tokenizer.quoteChar('"');
      }
  
      public Token peekToken()
      {	
          if(m_ioexn != null)
              return null;
          try
          {
              m_tokenizer.nextToken();
          }
          catch(IOException e)
          {
              m_ioexn = e;
              return null;
          }
          if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
              return null;
          Token token = new Token(m_tokenizer);
          m_tokenizer.pushBack();
          return token;
      }
  
      public boolean hasNext()
      {
          if(m_ioexn != null)
              return false;
          try
          {
              m_tokenizer.nextToken();
          }
          catch(IOException e)
          {
              m_ioexn = e;
              return false;
          }
          if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
              return false;
          m_tokenizer.pushBack();
          return true;
      }
  
      /** Return the most recently caught IOException, if any,
       *
       * @return
       */
      public IOException getIOException()
      {
          return m_ioexn;
      }
  
      public Token next()
      {
          try
          {
              m_tokenizer.nextToken();
          }
          catch(IOException e)
          {
              m_ioexn = e;
              return null;
          }
  
          Token token = new Token(m_tokenizer);
          return token;
      }
  
      public void remove()
      {
      }
  }
  