Upgrade Cats dependency to 0.7

[alexandru]

Cats 0.7 is out and dependency should be upgraded.

[lukestephenson]

Note that monix 2.0-RC11 did not work with cats 0.7. There are breaking changes.

[error] (run-main-0) java.lang.AbstractMethodError: monix.cats.EvaluableInstances$$anon$1.tailRecM(Ljava/lang/Object;Lscala/Function1;)Ljava/lang/Object;
java.lang.AbstractMethodError: monix.cats.EvaluableInstances$$anon$1.tailRecM(Ljava/lang/Object;Lscala/Function1;)Ljava/lang/Object;
    at cats.free.Free.foldMap(Free.scala:131)
    at cats.free.Free.foldMapUnsafe(Free.scala:142)
    at demo.AppInterpreter.run(AppInterpreter.scala:12)
    at app.Main$$anonfun$main$1.apply$mcV$sp(Main.scala:20)
    at app.Main$.timed(Main.scala:26)
    at app.Main$.main(Main.scala:17)
    at app.Main.main(Main.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)

In my example, I was using

script.foldMapUnsafe(xxx)

so I was surprised to see cats trying to call tailRecM on the monix cats Monad. Could be a bug in cats.

[lukestephenson]

I'm now getting some test failures. To resolve this I'm looking to supply custom equality methods for the checking (it's comparing two Task[Task[Int]] and only executing the outer task (unless for the logic to be correct both should be Suspend or BindSuspend).

[info] - CoflatMap[Task[Int]].coflatMap.coflatten throughMap *** FAILED ***
[info]   Falsified after 0 passed tests. (Checkers.scala:36)
[info]   > Labels of failing property:
[info]   (Suspend(<function0>) ?== BindSuspend(<function0>,<function1>)) failed
[info]   > ARG_0: Suspend(<function0>)
[info]     minitest.laws.Checkers$class.check(Checkers.scala:36)
[info]     monix.cats.TaskLawsSuite$.check(TaskLawsSuite.scala:26)

Hopefully I can submit a PR soon.

[alexandru]

Unfortunately I'm blocked by this issue in Cats. ATM FlatMap / Monad instances are no longer implementable for Observable because of tailRecM: typelevel/cats#1329

[alexandru]

OK, I managed to reconfigure ScalaCheck, such that the tailRecM tests pass for Observable. I'm using the following parameters:

    Parameters.default
      .withMinSuccessfulTests(10)
      .withMaxDiscardRatio(50.0f)
      .withMaxSize(6)

Not good though, because it weakens the tests. I hope Cats will provide a solution for monads that do not want to implement tailRecM in the future.

[alexandru]

Deployed in 2.0-RC13