options {
LOOKAHEAD=1;
}

PARSER_BEGIN(Parser)
public class Parser {}
PARSER_END(Parser)

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

TOKEN :
{
        < EOL: "\n" >
|       < PLUS: "+" >
|       < MULTIPLY: "*" >
|       < LPAR: "(" >
|       < RPAR: ")" >
|       < CONSTANT: ( <DIGIT> )+ >
|       < #DIGIT: ["0" - "9"] >
}

IASTNode Start() :
{ IASTNode t;}
{
    t = exp() <EOL>        { return t; }
}

IASTNode exp() :
{ IASTNode l,r; 
  Token x; }
{
    l = term() [ <PLUS> r = exp() { l = new ASTAdd(l,r);}]

   { return l; }
}

IASTNode term() :
{ IASTNode l,r; Token x; }
{
    l = factor() [ <MULTIPLY> r = term() { l = new ASTMul(l,r);} ]

   { return l; }
}

IASTNode factor() :
{ IASTNode e; }
{
    <CONSTANT> 

         {  e = new ASTNum(Integer.parseInt(token.image)); return e;}

|   <LPAR> e = exp() <RPAR> 

         { return e; }
}