ifPackageKey :: InterfaceFile -> PackageKey
ifPackageKey if_ =
  case ifInstalledIfaces if_ of
    [] -> error "empty InterfaceFile"
    iface:_ -> modulePackageKey $ instMod iface
ifPackageKey :: InterfaceFile -> PackageKey
ifPackageKey if_ =
  case ifInstalledIfaces if_ of
    [] -> error "empty InterfaceFile"
    iface:_ -> modulePackageKey $ instMod iface
ifPackageKey if_ =
  case ifInstalledIfaces if_ of
    [] -> error "empty InterfaceFile"
    iface:_ -> modulePackageKey $ instMod iface