Test a subset of laws / exclude some laws

[dschrempf]

Hello,

I have a zip-like applicative instance of a tree (similar to a ZipList), and I would like to test the applicative laws. I know that

Homomorphism
pure f <*> pure x ≡ pure (f x)

holds, but the test suite hangs (because pure x is an infinite tree).

Is there a way to test the the applicative laws but exclude this one test. In general, is there a way to perform a test on a subset of laws?

Thank you!

[andrewthad]

There is not currently a way to do this. In the interest of pragmatism, I'd think I'd be fine with a PR adding applicativeWithoutHomomorphismLaws, which would just not do that one test. Alternatively, if you're using tasty, you might be able to use a flag to exclude tests matching a certain pattern, or you may be able to modify the options (adding the exclusion) after tasty has parsed the options.

[andrewthad]

Sorry, didn't mean to close.

[dschrempf]

OK. In this case, I propose using the following function (works very well here):

filterLaws :: [String] -> Laws -> Laws
filterLaws xs (Laws tn ps) = Laws tn [ (n, p) | (n, p) <- ps, n `notElem` xs ]

Then, one can use, e.g.,

      lawsCheck (filterLaws ["Homomorphism"] $ applicativeLaws (Proxy :: Proxy (ZipTree String)))

Or maybe excludeLaws would be more appropriate.