javacc 簡單的四則運算

JAVACC 實作四則運算

Simple.JJ檔案

options
{
  STATIC = false;
  DEBUG_PARSER = true;
}

PARSER_BEGIN(Simple)
package cn.com.XXX.test.simple4;
public class Simple
{
  public static void main(String [] args) throws ParseException, TokenMgrError
  {
    Simple parser = new Simple(System.in);
    System.out.println(parser.start());
  }
}

PARSER_END(Simple)
SKIP :
{
  " "
}

SKIP :
{
  "\n"
| "\r"
| "\r\n"
}

TOKEN :
{
    < PLUS : "+" >
 |  < MINUS : "-" >
 |  < TIMES : "*" >
 |  < DIVES : "/" >
}

TOKEN :
{
  < NUMBER : ([ "0"-"9" ])+ >
}

TOKEN :
{
  < END : "=" >
}



// start --> expression()< EOF>
// expression -->  term() ( + term() | - term() )
// term() --> primite() ( * primite() | / primite() )
// primite() --> < NUMBER> 

int start():
{
  int rtn = 0;
}
{
  rtn = term()< END>
  {
   return rtn;
  }
}


int expression () :
{
  int value1 = 0;
  int value2 = 0;
}
{
  value1 = term()
  (
    	< PLUS> value2 = term() {value1 = value1+value2; }

	|
		<MINUS> value2 = term() { value1 = value1 - value2; }
  )* 
  {
    return value1;
  }
}



int term() :
{
  int value1 = 0;
  int value2;
}
{
  value1 = primite()
  (

   	   < TIMES> value2 = primite() {value1 = value1* value2; }
	|  < DIVES> value2 = primite() {value1 = value1 / value2;}
	 
  )*
 {
	return value1;
 }
} 


int primite():
{
  Token t;
  int sum = 0;
}
{
  t= < NUMBER > { return Integer.parseInt(t.image);}
| "(" sum = expression() { return sum;} ")"
}

           

幾年前為做示範，現場寫的一個簡單的四則運算，當然存在很多瑕疵，但隻是用來展現使用方式足夠了。

今天無意中發現了，感覺都有點生疏了，記錄一下。