[Haskell-cafe] The instability of Haskell libraries

Ivan Lazar Miljenovic ivan.miljenovic at gmail.com
Sun Apr 25 16:47:27 EDT 2010

Henning Thielemann <schlepptop at henning-thielemann.de> writes:
> My conclusion was: Never define orphan instances privately. If an
> instance cannot be added to the packages that provide the associated
> type or the class, then discuss the orphan instance with the maintainers
> of the type and the class and setup a package that provides that
> instance.

So you recommend having packages specifically for instances?

My main problem with this is if you want a custom variant of that
instance.  Let's take FGL graphs for example with instances for
QuickCheck's Arbitrary class.  Maybe you want arbitrary graphs that are
simple, or maybe multiple edges are fine.  Even when considering
Arbitrary instances for something like String you may wish to have a
custom variant that makes sense for what you're testing.

My conclusion: it is not possible to have hard-and-fast conclusions for
things like this :p

Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com

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