class Walker extends TreeParser;

options {
     buildAST=true;
     importVocab=P;
//     ASTLabelType = "MyAST";
}

tokens {
       EXPR="expr";
}

prog  : stmts 
      ;

stmts :  #(BLOCK {setASTNodeType("MyAST");}
	     stmtList)  
      ;

stmtList   :   stmt stmtList
	    |
	    ;

stmt  :  #(ASSIGN id expr)
	     { // checking goes here
	      }
      |  #(IFTHEN expr stmts)
      |  #(READ id )
      |  #(WRITE expr)
      ;


expr  : #(EQ expr expr)
      | #(NEQ expr expr)
      |! #(op:PLUS left:expr right:expr)
	       {//System.out.println("Creating node for + expr");
	        #expr = #(#[EXPR,"expr"], op, left, right);
		MyAST _expr = (MyAST)#expr, 
		      _left = (MyAST)#left,
		      _right = (MyAST)#right;
	        _expr.setExprType(10 + _left.getExprType() + _right.getExprType());
		}
      | #(MINUS expr expr)
      | ! #(t_op:TIMES t_left:expr t_right:expr)
               {//System.out.println("Creating node for + expr");
                #expr = #(#[EXPR,"expr"], t_op, t_left, t_right);
                MyAST _expr = (MyAST)#expr,
                      _left = (MyAST)#t_left,
                      _right = (MyAST)#t_right;
                _expr.setExprType(20 + _left.getExprType() +_right.getExprType());
                }
      | #(DIVIDE expr expr)
//      : MINUS^ (primary)
      |  id                                
      |  constant
      ;

id    :  i:ID   
	  {MyAST t= new MyAST();
           t.initialize(i);
	   t.setExprType(2);
	   #id = t;
	  }
      ;

constant :  n:NUM
             {MyAST t= new MyAST();
              t.initialize(n);
              t.setExprType(1);
              #constant = t;
             }
      ;