Frequently Asked Questions

Help! The IDE can’t figure out what the error type should be!

We provide a helper method errorIs which you can use to annotate the expected error type, which will help your IDE infer the error type of the following calls.

Note that the Coproduct instance of a sealed trait is alphabetically ordered!

sealed trait Sealed
case class C() extends Sealed
case class B() extends Sealed
case class A() extends Sealed

val either: Either[Sealed, Unit] = Left(C())
// either: Either[Sealed, Unit] = Left(C())

either.errorAsCoproduct.errorIs[A :+: B :+: C :+: CNil]
// res0: Either[A :+: B :+: C :+: CNil, Unit] = Left(Inr(Inr(Inl(C()))))

// Or for errorAsCoproduct specifically..
either.errorAsCoproduct[A :+: B :+: C :+: CNil]
// res1: Either[A :+: B :+: C :+: CNil, Unit] = Left(Inr(Inr(Inl(C()))))

How does the ZIO / Cats Effect integration work? Why do I not need an extra hotpotato-zio dependency and an import?

To improve user ergonomics, this project puts all typeclass instances inside the companion object. Do not worry! With optional dependencies like zio and cats-effect marked as optional, your project will not incur a dependency on them if you don’t already have it in your classpath!

To read more about this technique, see “No More Orphans” from 7minds.io

Known issues / Caveats?

• Compile time - due to the heavy use of shapeless (implicits), compile time of your project may suffer. It’s recommended that you use hotpotato where it matters, and use sealed traits when it is sufficient.