Error messages referring to inferred capabilities are not helpful

[b-studios]

In the following example the generated error message refers to an implicitly inferred capability. It is never bound and impossible to understand:

effect Yield(): Unit

def foo() = {
  var x in global = 42;
  x = x + 1
  def bar(): Unit / {} = do Yield();
  println(x)
  fun() { bar() }
}

def main() = try {
  foo() 
} with Yield { resume(()) }

The inferred type of foo also mentions the capability (which is equally hard to understand)

We need a proper way to refer to capabilities that are introduced for effects.