[Haskell-cafe] Oprhan instances (Was: Some help needed to start Haskell with Yi)

[Daniel Fischer]

Am Donnerstag 26 November 2009 19:44:11 schrieb Joachim Breitner:
> Hi,
>
> Am Donnerstag, den 19.11.2009, 03:29 +0100 schrieb Daniel Fischer:
> > Perhaps the very best method is to contact the author/maintainer of
> > packageY and say you need the instance.
>
> but this might not be desirable when the data type and the class
> definition are in separate packages, and the author of the package with
> the data type is not willing to add additional dependencies to his
> package (which is a valid goal).
>
> Or how would you proceed if you need a Binary instance (from package
> binary) for UTCTime (from package date), as I do in arbtt?
>
> Greetings and thanks,
> Joachim

To: author/maintainer
Re: instance Foo Bar

Dear a/m,

I need instance Foo Bar for my project.
If you consider such an instance of general use, it would be nice if you'd upload a new 
version of your package with that instance to hackage soon.
Otherwise, I'll declare an instance in my own package.
Please let me know your decision,
Regards,
me

Case 1:
I think it would be a good idea to have the instance in my package, I'll upload the new 
version tomorrow.
Regards,
a/m

Problem solved, no orphan instance, great :)

Case 2:
For this and that reason, I don't want to include that instance in my package.
Sorry to force an orphan instance upon you.
Regards,
a/m

Unfortunately you'll have to declare an orphan instance, but at least you know that it's 
unlikely to break anything soon.

Case 3:
No answer within x days :(

Declare an orphan instance and hope for the best.


Better than declaring an orphan instance without asking the very day the author of package 
x realises that such an instance would be quite useful and adds it, isn't it?

Cheers,
Daniel