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remove localSpanViaKleisli since it's now available in natchez-mtl 0.3.1 #19

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Feb 15, 2023
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remove localSpanViaKleisli since it's now available in natchez-mtl 0.3.1 #19

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45 changes: 0 additions & 45 deletions core/src/main/scala/com/dwolla/tracing/instances/package.scala
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Original file line number Diff line number Diff line change
@@ -1,58 +1,13 @@
package com.dwolla.tracing

import cats._
import cats.data._
import cats.effect.{Trace => _, _}
import cats.mtl._
import natchez._

package object instances extends LocalInstances

package instances {
trait LocalInstances {
/** When fulfilling a effect-polymorphic function demanding an implicit
* `Local[F, Span[F]]` with `[F[_], A] =>> Kleisli[F, Span[F], A]`,
* the implicit instances provided by cats-mtl don't quite fit. The
* code demands
* `Local[Kleisli[F, Span[F], *], Span[Kleisli[F, Span[F], *]]`,
* but `Local.baseLocalForKleisli` returns
* `Local[Kleisli[F, Span[F], *], Span[F]]` (the `E` parameter is
* wrong), and `Local.localForKleisli` requires an implicit
* `Local[F, Span[Kleisli[F, Span[F], *]]`, which we don't have.
*
* However, it's safe to `imap` the `Local[Kleisli[F, Span[F], *], Span[F]]`
* returned by `Local.baseLocalForKleisli` using `Kleisli.liftK` and
* `Kleisli.applyK`. `Kleisli.liftK` will turn `Span[F]` into
* `Span[Kleisli[F, Span[F], *]]`, which, when run, will ignore any
* `Span[F]`s passed to each `Kleisli[F, Span[F], *]`. We take
* advantage of that by immediately `mapK`ing it back to `Span[F]`,
* applying a no-op span that we know will never actually be used.
*
* This instance is law-tested in [[https://github.com/tpolecat/natchez/pull/713 tpolecat/natchez#713]],
* so it's believed to be a lawful instance.
*
* TODO Remove when [[https://github.com/tpolecat/natchez/pull/713 tpolecat/natchez#713]] is merged and released
*
* @param F the `MonadCancel[F, _]` instance demanded by `Span[F].mapK`
* @tparam F the effect in which to operate
* @return a `Local[Kleisli[F, Span[F], *], Span[Kleisli[F, Span[F], *]]]` instance
*/
implicit def localSpanViaKleisli[F[_]](implicit F: MonadCancel[F, _]): Local[Kleisli[F, Span[F], *], Span[Kleisli[F, Span[F], *]]] =
new Local[Kleisli[F, Span[F], *], Span[Kleisli[F, Span[F], *]]] {
override def local[A](fa: Kleisli[F, Span[F], A])
(f: Span[Kleisli[F, Span[F], *]] => Span[Kleisli[F, Span[F], *]]): Kleisli[F, Span[F], A] =
fa.local {
f.andThen(_.mapK(Kleisli.applyK(Span.noop[F])))
.compose(_.mapK(Kleisli.liftK))
}

override def applicative: Applicative[Kleisli[F, Span[F], *]] =
Kleisli.catsDataApplicativeForKleisli

override def ask[E2 >: Span[Kleisli[F, Span[F], *]]]: Kleisli[F, Span[F], E2] =
Kleisli.ask[F, Span[F]].map(_.mapK(Kleisli.liftK))
}

/**
* Given an `IOLocal[E]`, provides a `Local[IO, E]`.
*
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