RelationalExpression.scala

lazy val predicate: PackratParser[Expression] =
    predicate ~ ("and" ~> relExpression) ^^ {case l ~ r => AndExp(l, r)} |
    predicate ~ ("or" ~> relExpression) ^^ {case l ~ r => OrExp(l, r)} |
    relExpression

lazy val relExpression: PackratParser[Expression] =
    relExpression ~ ("gt" ~> expression) ^^ {case l ~ r => GreaterThanExp(l, r)} |
    relExpression ~ ("lt" ~> expression) ^^ {case l ~ r => LessThanExp(l, r)} |
    relExpression ~ ("eq" ~> expression) ^^ {case l ~ r => EqualToExp(l, r)} |
    relExpression ~ ("ne" ~> expression) ^^ {case l ~ r => NotEqualToExp(l, r)} |
    relExpression ~ ("ge" ~> expression) ^^ {case l ~ r => GreaterOrEqualToExp(l, r)} |
    relExpression ~ ("le" ~> expression) ^^ {case l ~ r => LessOrEqualToExp(l, r)} |
    expression