javacc学习-jjtree例子（二）

PARSER_BEGIN(Eg1)

/** An Arithmetic Grammar. */
public class Eg1 {

  /** Main entry point. */
  public static void main(String args[]) {
    System.out.println("Reading from standard input...");
    Eg1 t = new Eg1(System.in);
    try {
      SimpleNode n = t.Start();
      n.dump("");
      System.out.println("Thank you.");
    } catch (Exception e) {
      System.out.println("Oops.");
      System.out.println(e.getMessage());
      e.printStackTrace();
    }
  }
}

PARSER_END(Eg1)


SKIP :
{
  " "
| "\t"
| "\n"
| "\r"
//忽略注释符//开头的行和/*注释的
| <"//" (~["\n","\r"])* ("\n"|"\r"|"\r\n")>
| <"/*" (~["*"])* "*" (~["/"] (~["*"])* "*")* "/">
}

TOKEN : /* LITERALS */
{
  < INTEGER_LITERAL:
        <DECIMAL_LITERAL> (["l","L"])?
      | <HEX_LITERAL> (["l","L"])?
      | <OCTAL_LITERAL> (["l","L"])?
  >
|
//浮点TOKEN
  < #DECIMAL_LITERAL: ["1"-"9"] (["0"-"9"])* >
|
//十六进制TOKEN
  < #HEX_LITERAL: "0" ["x","X"] (["0"-"9","a"-"f","A"-"F"])+ >
|
//十进制TOKEN
  < #OCTAL_LITERAL: "0" (["0"-"7"])* >
}

TOKEN : /* IDENTIFIERS */
{
  < IDENTIFIER: <LETTER> (<LETTER>|<DIGIT>)* >
|
  < #LETTER: ["_","a"-"z","A"-"Z"] >
|
  < #DIGIT: ["0"-"9"] >
}

/** Main production. */
SimpleNode Start() : {}
{
  Expression() ";"
//jjthis返回是一个simplenode类型的树操作
  { return jjtThis; }
}

/** An Expression. */
void Expression() : {}
{
  AdditiveExpression()
}

/** An Additive Expression. */
void AdditiveExpression() : {}
{
  MultiplicativeExpression() ( ( "+" | "-" ) MultiplicativeExpression() )*
}

/** A Multiplicative Expression. */
void MultiplicativeExpression() : {}
{
//匹配类似(IDENTIFIER|INTEGER_LITERAL)*( ( "*" | "/" | "%" ) (IDENTIFIER|INTEGER_LITERAL)*
  UnaryExpression() ( ( "*" | "/" | "%" ) UnaryExpression() )*
}

/** 返回TOKEN描述 */
void UnaryExpression() : {}
{
  "(" Expression() ")" | Identifier() | Integer()
}

/** An Identifier. */
void Identifier() : {}
{
  <IDENTIFIER>
}

/** An Integer. */
void Integer() : {}
{
  <INTEGER_LITERAL>
}