recommender :: Playlist -> (Song -> SongName)
recommender' pls = helper sng
    where
        helper :: Song -> SongName
        helper song
            | rs == [] = song
            | otherwise = fst $ dropWhile (Song -> r) rs

        authName :: Song -> AuthorName
        authName song = map (\(Song aut _ _ _) -> aut) song

        rs :: SongName
        rs = getNextSong $ song

        getNextSong :: Song -> SongName
        getNextSong song = dropWhile ((song /= pl) -> pl) pls