Error during derivation for recursive data types #144
Comments
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It looks like it might be a bug. I will try it out later, but in the meantime - we have a test for |
I just tried it and it doesn't work either (the implementation is functionally identical except for some additional cases in my code). |
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Ok, thanks for trying 👍 |
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I'm not sure if I ran into into the same issue but I have issues with recursion as well: // THIS WORKS
@Test
def testRec: Unit =
final case class Rec(as: Vector[Rec])
Typeable[Rec]
// THIS DOES NOT WORK
final case class Rec2(as: Vector[Rec2])
@Test
def testRec2: Unit =
Typeable[Rec2]is this expected behavior? The second example is generally how I'd summon the Typeable instance in a different piece of code than the case classes |
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@tschuchortdev sorry that I didn't see this sooner, but you need to make the coproduct instances by-name if you want it to work with recursive types. The same applies to our example in the tests: given coproductFunctorK[D[_[_]]] (using cInst: => K11.CoproductInstances[FunctorK, D]): FunctorK[D] with {
extension[F[_]] (df: D[F])
override def mapK[G[_]](fg: [A] => F[A] => G[A]): D[G] =
cInst.fold(df) {
[t[f[_]] <: D[f]] => (caseFunctorK: FunctorK[t], _case: t[F]) =>
caseFunctorK.mapK(_case)(fg)
}
}@@ -333,7 +333,7 @@ object FunctorK:
given [T]: FunctorK[K11.Id[T]] with
def mapK[A[_], B[_]](at: A[T])(f: A ~> B): B[T] = f(at)
- given functorKGen[H[_[_]]](using inst: K11.Instances[FunctorK, H]): FunctorK[H] with
+ given functorKGen[H[_[_]]](using inst: => K11.Instances[FunctorK, H]): FunctorK[H] with
def mapK[A[_], B[_]](ha: H[A])(f: A ~> B): H[B] =
inst.map(ha)([t[_[_]]] => (ft: FunctorK[t], ta: t[A]) => ft.mapK(ta)(f)) |
joroKr21
added
bug
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@agaro1121 that's a different issue. |
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I'm trying to generically derive instances of
FunctorKfor recursive data structures:Given following example
an error will be thrown by the compiler:
A similar problem also appears for classes like this:
Note that an almost identical error with
mkProductInstancescan be produced depending on the order of summoning (Foo2orFoo2Recfirst).I believe the error might occur because of an infinite recursion in the derivation logic that reaches the inlining depth limit. When the inlining limit is reached, further calls to the inline function (
ErasedCoproductInstances.apply?) are no longer inlined, perhaps causing the types to no longer match. A different error message, which I am unfortunately unable to reproduce, suggested this to me.I understand that recursive data structures were already addressed in #40, so I'm not sure if it's a bug in the library or in my own code.
Library version: 3.3.0
Scala version: 3.2.1
IntelliJ plugin version: 2023.1.548
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