allow variable binding in alternative pattern #182
Description
= Code =
abstract class Arith
case class Plus(l: Arith,r: Arith) extends Arith
case class Prod(l: Arith,r: Arith) extends Arith
case class Number(n: Int) extends Arith
case class Var(x: String) extends Arith
def isEquation(expr: Arith): Boolean = expr match {
case Plus(l,r) | Prod(l,r) => isEquation(l) || isEquation(r)
case Number(_) => false
case Var(_) => true
}
val expr = Plus(Number(1),Prod(Number(2),Number(3)))
isEquation(expr)= What happened =
At compilation the following error is prompt
9: error: illegal variable in pattern alternative
case Plus(l,r) | Prod(l,r) => isEquation(l) || isEquation(r)
^ Though, this is normal as or-patterns are not allowed to bind variables.
= Enhancement =
As the case classes Plus and Prod both accept a left and right argument of type Arith, it would be nice to allow binding of variables in the or-pattern definition.