Curry the typical pattern of matching equals by pairs, preserving exhaustiveness checking while reducing the boilerplate in each case.

For example, this is unsafe:

(l, r) match {
  case (Left(l1), Left(l2)) => l1 == l2
  case (Right(r1), Right(r2)) => r1 == r2
  case _ => false
}

because the third case disables exhaustiveness checking. And the easier it is to make this mistake, the stronger impulse to create the situation where it can occur, because the cost of writing out the false cases is quadratic.

With this function, the above would be written

match2(fallback = false) {
  case Left(l1) => {case Left(l2) => l1 == l2}
  case Right(r1) => {case Right(r2) => r1 == r2}
}

which preserves exhaustiveness checking for the left argument, which is perfectly sufficient for writing equals functions.