Define laws for Traversable #442
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zalbia
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| /** | ||
| * Traversing by `Id` is equivalent to mapping. | ||
| */ | ||
| val identityLaw: LawsF.Covariant[DeriveEqualTraversable, Equal] = { |
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You can implement your own law until we add one to ZIO Test.
| @@ -269,11 +270,25 @@ trait Traversable[F[+_]] extends Covariant[F] { | |||
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| object Traversable extends LawfulF.Covariant[DeriveEqualTraversable, Equal] { | |||
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| // need to implement natural transformations for this property? | |||
| // val naturalityLaw: LawsF.Covariant[DeriveEqualTraversable, Equal] = ??? | |||
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I think we can restate this as a fusion law that if we have F[G[H[A]]] where F is traversable and G and H have IdentityBoth and Covariant then we can individually flip twice or we can create a composed instance and flip the whole thing once.
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Thanks for the big tip!
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@adamgfraser can you check if I'm going in the right direction so far? AFAICT, there's still lots of work to be done, like making it so the |
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- make newtypes for `Nested` functors and functor `Product`s - make instances needed for everything to work - add type ascriptions to make compiler happy in Traversable.scala
| * | ||
| * If F[_] and G[_] are both IdentityBoth, then Nested[F, G, *] is also an IdentityBoth. | ||
| * | ||
| * If F[_] and G[_] are both Traversable, then Nested[F, G, *] is also a Traversable. |
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I think it would be nice to add tests for that at CovariantSpec, IdentityBothSpec, TraversableSpec
can copy it from my branch:
Badmoonz@6df1301#diff-82e9bed52abfcc1cabd8fb86c811dcab611fbd08d2ff81124a90af2fb0a78834R21
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So I tried to add the ones for CovariantSpec & IdentityBothSpec, and they led to the same build errors for 2.11 in #449. Any idea on how to make them work?
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After some research , I've found solution : make alias type for nested
{
type T[+A] = Nested[Vector, Option]
testM("Nested[vector,option]")(checkAllLaws(Traversable)(GenFs.nested(GenF.vector, GenF.option) : GenF[T, Random with Sized] , Gen.anyInt))
}
It looks like scala 2.11 compiler cannot derive type CapF[_[_[_]]] from first argument GenFs.nested(GenF.vector, GenF.option) which has type GenF[(lambda[+A] = Nested[Vector, Option, A)#lambda, Random with Sized].
I supposed that's because it has lambda type param, but CovariantSpec has tuple, either gens that also return GenF with lambda type param, and it works well
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@adamgfraser @zalbia @sideeffffect This one ready to merge (aside from merge conflicts)??? |
# Conflicts: # core/shared/src/test/scala/zio/prelude/TraversableSpec.scala
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@jdegoes it may turn out we may need just one law for Traversable #373 (comment) |
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We should merge #449 once the PR passes checks. |
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@zalbia 👍 |
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ok, i will update und fix #449 today |
closes #373