Add Contravariant instance for Eq and test Show instance. #1211
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Perhaps we could do a heuristic test by generating a bunch of |
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👍 great! |
| * Create an approximation of Eq[Eq[A]] by generating 100 values for A | ||
| * and comparing the application of the two eqv functions | ||
| */ | ||
| implicit def catsLawsEqForEq[A](implicit arbA: Arbitrary[(A, A)], booleanEq: Eq[Boolean]): Eq[Eq[A]] = new Eq[Eq[A]] { |
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I don't really think we need the Eq[Boolean] here. I think we assume that primitives are okay to compare directly.
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That makes sense, I adapted catsLawsEqForOrder where an Eq[Int] is used.
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As far I can tell this seemed to be the only missing
Contravariantinstance.#579 also mentioned
StateT, but I think only anIndexedStateTwould have aContravariant(that's also why there is noProfunctorinstance, see #1067).I don't think it is possible to test the instance for
Eq, sinceCovariantTestswould need anArbitrary[Eq[A]]and anEq[Eq[A]]?