Other libraries are better.
Haskellの文字列型同士の変換が欲しい場合はconvertibleかstring-conversionsを使うと良い感じです - ncaq
simple and easy haskell string transform wrapper.
toStringtoByteStringStricttoByteStringLazytoShortByteStringtoTextStricttoTextLazy
It wrapper expect that ByteString encode is utf-8.