/* expr/javacc/Exprtree.jjt in JavaCC tree-builder format
   Build with 

	jjtree Exprtree.jjt
	javacc Exprtree.jj
	javac *.java

   Run as
        
        java Expr 

   Enter e.g. 4 * 3 followed <ctrl-D> on Unix or <ctrl-Z> on Windows.
   A rather crude abstract syntax tree will be printed in response.
 */

options {
LOOKAHEAD=1;
}

PARSER_BEGIN(Expr)

public class Expr {
  public static void main(String args[]) throws ParseException {
    Expr parser = new Expr(System.in);
    System.out.print("Enter Expression: ");
    SimpleNode tree = parser.Main();
    tree.dump("");
  }
}
PARSER_END(Expr)

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


TOKEN : /* operators */
{ < PLUS  : "+" >
| < MINUS : "-" >
| < TIMES : "*" >
| < LPAR  : "(" >
| < RPAR  : ")" >
}

TOKEN : /* constants and variables */
{ < CSTINT  : ( <DIGIT> )+ >
| < #DIGIT  : ["0" - "9"] >
| < NAME    : <LETTER> ( <DIGIT> | <LETTER> )* >
| < #LETTER : ["a"-"z", "A"-"Z"] >
}

SimpleNode Main() : 
{}
{
  Expr() <EOF> { return jjtThis; }
	
}

void Expr() :
{}
{
  Term() ( ( <PLUS> | <MINUS> ) Term() )*
}

void Term() :
{ }
{
  Factor() ( <TIMES> Factor() )*
}

void Factor() :
{ }
{
   <NAME>
 | <CSTINT> 
 | <MINUS> <CSTINT>
 | <LPAR> Expr() <RPAR>
}