Recipe for Writing a Parser

Example:

public class ListParser<P extends ListProcessor>
{
  private static final TerminalSymbolType OPEN = TerminalSymbolType.delimiter("(");
  private static final TerminalSymbolType CLOSE = TerminalSymbolType.delimiter(")");
  private static final TerminalSymbolType COMMA = TerminalSymbolType.delimiter(",");
  
  private NonTerminalSymbol<P> _list;
  
  public ListParser()
  {
    _list = new NonTerminalSymbol<P>("list");
    NonTerminalSymbol<P> element = new NonTerminalSymbol<P>("element");
    TerminalSymbol<P> atom = createAtom();
    TerminalSymbol<P> open = new TerminalSymbolByText<P>(OPEN);
    TerminalSymbol<P> comma = new TerminalSymbolByText<P>(COMMA);
    TerminalSymbol<P> close = new TerminalSymbolByText<P>(CLOSE);
  }
}

Example:

  public ListParser()
  {
    ...
    _list.definedBy(open
                   .followedBy(element.zeroOrMoreTimesSeparatedBy(comma))
                   .followedBy(close));
    element.definedBy(atom.or(_list));
  }

Example:

  public void parse(Reader reader, P processor)
  {
    SimpleLexer lexer = new SimpleLexer(OPEN, CLOSE, COMMA);
    _list.process(lexer.createTokenIterator(reader), processor);
  }

  new ListParser<Processor>().parse(reader, new Processor() {});

Example:

public interface ListProcessor extends Processor
{
  public void startList();
  
  public void handleAtom(String atom);
  
  public void finishList();
}

Example:

public class ListParser<P extends ListProcessor>
{
  private static final Pattern ATOM_PATTERN = Pattern.compile("[a-z][a-zA-Z0-9]*");
  ...
  public ListParser()
  {
    _list = declareList();
    NonTerminalSymbol<P> element = new NonTerminalSymbol<P>("element");
    TerminalSymbol<P> atom = createAtom();
    TerminalSymbol<P> open = new TerminalSymbolByText<P>(OPEN);
    TerminalSymbol<P> comma = new TerminalSymbolByText<P>(COMMA);
    TerminalSymbol<P> close = new TerminalSymbolByText<P>(CLOSE);
    
    _list.definedBy(open
                   .followedBy(element.zeroOrMoreTimesSeparatedBy(comma))
                   .followedBy(close));
    element.definedBy(atom.or(_list));
  }
  
  private NonTerminalSymbol<P> declareList()
  {
    return new NonTerminalSymbol<P>("list")
      {
        @Override
        protected void preProcess(P processor)
        {
          processor.startList();
        }

        @Override
        protected void postProcess(P processor)
        {
          processor.finishList();
        }
      };
  }

  private TerminalSymbol<P> createAtom()
  {
    return new TerminalSymbolByType<P>(NormalToken.NORMAL_TOKEN)
      {
        @Override
        protected void process(Token token, P processor)
        {
          String atom = token.getText();
          if (ATOM_PATTERN.matcher(atom).matches() == false)
          {
            throw new IllegalArgumentException("Not a valid atom.");
          }
          processor.handleAtom(atom);
        }
      };
  }

• pretty formatting,
• interpreting,
• building Java objects,
• compilation.

Example:

public class ListBuilder implements ListProcessor
{
  private final Stack> _stack = new Stack>();
  private List