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

Daniel Fischer daniel.is.fischer at web.de
Thu Nov 26 14:32:11 EST 2009

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,

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

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.

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?


More information about the Haskell-Cafe mailing list