Scala 3 experimental checked exceptions question

Question
1

I originally asked in a discussion in Scala 3 GitHub, but I think this may be a better place for the question.

I’m trying to understand how the capability-based tracking of exceptions scale as you combine functions that use capabilities.

Following Capture Checking, I wrote this:

import caps.Capability
import language.experimental.captureChecking
import language.experimental.saferExceptions

class E1 extends Exception, Capability
class E2 extends Exception, Capability
class E3 extends Exception, Capability
class E4 extends Exception, Capability

def f1(): Unit throws E1 =
  throw E1()

def f2(): Unit throws E2 =
  throw E2()

def f3(): Unit throws E3 =
  throw E3()

def f4(): Unit throws E4 =
  throw E4()

def f5(): Unit throws E3 | E4 =
  f3()
  f4()

def f6(): Unit throws E1 | E2 | E3 | E4 =
  f5()
  f2()
  f1()

Ideally I shouldn’t have to list all of the exception types in f6. From the capture checking page linked above I thought I could do something like:

def f6: Unit^{f5, f2, f1} =
  f5()
  f2()
  f1()

But this generates a few errors.. Is something like this allowed? What’s the right syntax?

Thanks.