lookupPackageName :: Package pkg => PackageIndex pkg -> PackageName -> [pkg]
lookupPackageName index name =
  [ pkg | pkg <- lookup index name
        , packageName pkg == name ]
lookupPackageName :: Package pkg => PackageIndex pkg -> PackageName -> [pkg]
lookupPackageName index name =
  [ pkg | pkg <- lookup index name
        , packageName pkg == name ]
lookupPackageName index name =
  [ pkg | pkg <- lookup index name
        , packageName pkg == name ]