mapM_ for bytestring

[Henning Thielemann]

On Sun, 1 Sep 2013, Artyom Kazak wrote:

> On Sun, 01 Sep 2013 22:55:10 +0400, Henning Thielemann <lemming at henning-thielemann.de> wrote:
>
>> A possible solution might be fusion rules for ByteString.unpack and mapM_.
>
> Except that such rules would require a hand-written version of mapM_ anyway.
>
> I agree that it can be written, it’s just that I don’t see why it should be 
> in some obscure place instead of Data.ByteString.

This rule should of course be part of Data.ByteString. RULES are similar 
to class instances and like orphan instances, orphan rules are a bad idea.