Pattern Match “return” value

Question

Why is it not possible to chain pattern matching constructs? For instance, the following is legal, if nonsensical,

val a = ADT(5)

val b = a match {
  case          


        

Answer 1

Yes it should work, because (almost) everything in Scala is an expression and every expression can be used as a pattern match.

In this case the pattern match is an expression, so it can be used by another "chained" pattern match. But the compiler doesn't like it.

Giving the compiler a little hint with parentheses helps:

case class ADT(value: Int)

val a = ADT(5)

(a match {
  case ADT(a) if a > 4 => ADT(a * 3)
  case ADT(a) => ADT(a + 1)
}) match {
  case ADT(a) if a > 13 => println(a)
  case _ => {}
}