lookupPackageId :: PackageIndex a -> PackageId -> Maybe a
lookupPackageId index pkgid = case lookupSourcePackageId index pkgid  of
    []    -> Nothing
    [pkg] -> Just pkg
    _     -> error "Distribution.Simple.PackageIndex: multiple matches found"

-- | Does a lookup by source package name.
--
lookupPackageId :: PackageIndex a -> PackageId -> Maybe a
lookupPackageId index pkgid = case lookupSourcePackageId index pkgid  of
    []    -> Nothing
    [pkg] -> Just pkg
    _     -> error "Distribution.Simple.PackageIndex: multiple matches found"

-- | Does a lookup by source package name.
--
lookupPackageId index pkgid = case lookupSourcePackageId index pkgid  of
    []    -> Nothing
    [pkg] -> Just pkg
    _     -> error "Distribution.Simple.PackageIndex: multiple matches found"

-- | Does a lookup by source package name.
--