[Haskell-cafe] instance Binary UTCTime (Was: Oprhan instances)

Duncan Coutts duncan.coutts at googlemail.com
Mon Nov 30 10:02:26 EST 2009

On Mon, 2009-11-30 at 13:36 +0100, Bas van Dijk wrote:
> On Mon, Nov 30, 2009 at 11:35 AM, Duncan Coutts
> <duncan.coutts at googlemail.com> wrote:
> > Ah but flags are not allowed to change the public exported API of a
> > library.
> I wasn't aware of this. Where is this documented?

Hmm, I'm not sure it is actually. It should probably be mentioned in the
user guide section on conditionals.

You can tell it's wrong because there is no way for dependent packages
to specify that they need your package to export, say the Text instance.

> The reason I ask is because I have a small package on hackage that
> violates this:
> http://hackage.haskell.org/package/to-string-instances

It will fail if you install packages in the "wrong" order. To users this
will seem essentially random.


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