quote fn (x) { x }
quote fn (x, _y) { x }
quote fn ((x | _y)) { x }
quote fn {
  (()) { :error }
  ((x | _y)) { x }
  (_) { :error }
}
fn (x) { x }
fn (x, _y) { x }
fn ((x | _y)) { x }
fn {
  (()) { :error }
  ((x | _y)) { x }
  (_) { :error }
}
