p 210 shows some case classes, including abstract class Expr case class Binop(operator: String, left: Expr, right: Expr) extends Expr
I find that I cannot define a subclass of Binop; I get a compiler error:
case class RightAssociativeBinop(operator: String, left: Expr, right: Expr) extends Binop(operator, left,right)
<console>:7: error: error overriding value right in class Binop of type Expr; value right needs `override' modifier case class RightAssociativeBinop(operator: String, left: Expr, right: Expr) extends Binop(operator, left,right) ^
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