Orphan Instances with GHC 6.8

Adrian Hey ahey at iee.org
Wed Oct 17 12:03:54 EDT 2007

Hello again,

Adrian Hey wrote:
> Hello Folks,
> One thing different from 6.6 and 6.8 is I find that with -Wall
> I get a lot more warnings about orphan instances, even if the
> code has not changed.
> Has the definition of what an Orphan instance is changed?
> Or is this a bug? If so, is the bug in 6.6 or 6.8?
> I can make them go away with the -fno-warn-orphans flag,
> but I'm still curious as to why I didn't have to do this before.

Sorry, this situation seems more complex than this. I can't quite
figure out whats going on, in fact this but it may to be related
to some other change I've made in the code to get since 6.8.

The strange thing (to me) is that if I take exactly the same module
and use it in 2 different packages (which are compiled with the same
ghc options AFAIK), one gives me the orphan warning and one doesn't.
Does that make sense? (I.E. Is "Orphanness" somehow context dependent?)

Adrian Hey

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