I don't think so. There's no guarantee that future versions will maintain it, and I don't know that we want to take responsibility for continually checking on that.

David

On Feb 20, 2015 Simon Peyton Jones wrote:
> It'd be good to document this condition/invariant in the Haddocks, wouldn't it?!
>
> Simon
>
> |  -----Original Message-----
> |  From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of
> |  Herbert Valerio Riedel
> |  Sent: 19 February 2015 10:42
> |  To: Kazu Yamamoto
> |  Cc: libraries@haskell.org; ghc-devs@haskell.org
> |  Subject: Re: Behavior change of Data.Char
> |
> |  On 2015-02-19 at 06:19:18 +0100, Kazu Yamamoto (????) wrote:
> |  > It seems to me that some characters of GHC 7.10.1RC2 behave
> |  > differently from those of GHC 7.8.4:
> |  >
> |  >                           7.8.4   7.10.1RC2
> |  > isLower (char 170)        True    False
> |
> |  Fwiw, the motivation for that particular change may be (I'm just
> |  guessing here) to have the following condition hold:
> |
> |    \c -> isLower c `implies` (not . isLower . toUpper) c
> |
> |  i.e. if something is 'lower-case', then applying 'toUpper' should
> |  result in a character that is not 'lower-case' anymore. This didn't
> |  hold with 7.8.4's Unicode 6, but now holds with 7.10.1's Unicode 7
> |  definitions.
> |
> |  Cheers,
> |    hvr
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