I have a cabal package that exports a type NBT which might be useful for other developers. I've gone through the trouble of defining an Arbitrary instance for my type, and it would be a shame to not offer it to other developers for testing their code that integrates my work.

However, I want to avoid situations where my instance might get in the way. Perhaps the other developer has a different idea for what the Arbitrary instance should be. Perhaps my package's dependency on a particular version of QuickCheck might interfere with or be unwanted in the dependencies of the client project.

My ideas, in no particular order, are:

  • Leave the Arbitrary instance next to the definition of the type, and let clients deal with shadowing the instance or overriding the QuickCheck version number.
  • Make the Arbitrary instance an orphan instance in a separate module within the same package, say Data.NBT.Arbitrary. The dependency on QuickCheck for the overall package remains.
  • Offer the Arbitrary instance in a totally separate package, so that it can be listed as a separate test dependency for client projects.
  • Conditionally include both the Arbitrary instance and the QuickCheck dependency in the main package, but only if a flag like -ftest is set.

I've seen combinations of all of these used in other libraries, but haven't found any consensus on which works best. I want to try and get it right before uploading to Hackage.

haskell cabal quickcheck
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