Where do QuickCheck instances belong in a cabal package?

Question

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 t

Answer 1

The problem comes down to: how likely is it that someone using your library will be wanting to run QuickCheck tests using your NBT type?

If it is likely, and the Arbitrary instance is detailed (and thus not likely to change for different people), it would probably be best to ship it with your package, especially if you're going to make sure you keep updating the package (as for using a flag or not, that comes down to a bit of personal preference). If the instance is relatively simple however (and thus more likely that people would want to customise it), then it might be an idea to just provide a sample instance in the documentation.

If the type is primarily internal in nature and not likely to be used by others wanting to run tests, then using a flag to conditionally bring in QuickCheck is probably the best way to go to avoid unnecessary dependencies (i.e. the test suite is there just so you can test the package).

I'm not a fan of having QuickCheck-only packages in general, though it might be useful in some situations.