Stack-safe Coyoneda #1602

edmundnoble · 2017-04-12T05:10:28Z

Makes Coyoneda's map stack-safe, by keeping a list of functions and reversing it before applying them.
Breaking change.

adelbertc · 2017-04-12T05:12:29Z

free/src/main/scala/cats/free/Coyoneda.scala

-  /** The transformer function, to be lifted into `F` by `run`. */
-  val k: Pivot => A
+  /** The transformer functions, to be lifted into `F` by `run`. */
+  val k: List[Any => Any]


Given its signature should this be exposed? Seems like we should hide it.

I would say so, but the user should have the power to concatenate the lists IMO. Perhaps a scarier name?

Never mind, that doesn't sound useful. Making it private[cats] just in case we change it in future.

adelbertc · 2017-04-12T05:12:39Z

free/src/main/scala/cats/free/Coyoneda.scala

@@ -53,14 +57,18 @@ object Coyoneda {
  /** `F[A]` converts to `Coyoneda[F,A]` for any `F` */
  def lift[F[_], A](fa: F[A]): Coyoneda[F, A] = apply(fa)(identity[A])

-  /** Like `lift(fa).map(_k)`. */
-  def apply[F[_], A, B](fa: F[A])(k0: A => B): Aux[F, B, A] =
+  /** unsafe mang */


Maybe a better comment than this ;)

Omg I was removing it you fast person

codecov-io · 2017-04-12T05:52:32Z

Codecov Report

Merging #1602 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1602      +/-   ##
==========================================
+ Coverage   93.88%   93.88%   +<.01%     
==========================================
  Files         246      246              
  Lines        4088     4090       +2     
  Branches      154      154              
==========================================
+ Hits         3838     3840       +2     
  Misses        250      250

Impacted Files	Coverage Δ
free/src/main/scala/cats/free/Coyoneda.scala	`100% <100%> (ø)`	⬆️

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wedens · 2017-04-12T10:25:43Z

free/src/main/scala/cats/free/Coyoneda.scala

+  /** Creates a `Coyoneda[F, A]` for any `F`, taking an `F[A]`
+   * and a list of [[Functor.map]]ped functions to apply later
+   */
+  def unsafeApply[F[_], A, B](fa: F[A])(k0: List[Any => Any]): Aux[F, B, A] =


I don't think it (or anything with Any in it) should be public.

My bad, I was on my way to making this private. Not because of Any, but because it fixes List.

kailuowang · 2017-04-13T15:10:20Z

free/src/main/scala/cats/free/Coyoneda.scala


-  import Coyoneda.{Aux, apply}
+  def execute(a: Pivot): A =


Does this one need to be public?

Good question: it should in my opinion be public because a) it's as safe as exposing k previously and b) k was public before, which means users have had time to create use-cases that require using the function inside a Coyo on other values.

johnynek · 2017-04-13T15:52:48Z

I wonder if we want to just add code like:

sealed trait StackSafeFn[A, B] {
  def apply(a: A): B = StackSafeFn.run(this, a)
}
object StackSafeFn {
  private case class FromScala[A, B](fn: A => B) extends StackSafeFn[A, B]
  private case class Compose[A, B, C](first: StackSafeFn[A, B], second: StackSafeFn[B, C]) extends StackSafeFn[A, C]

  private def run[A, B](fn: StackSafeFn[A, B], a: A): B = ...
}

edmundnoble · 2017-04-13T17:30:19Z

@johnynek What we need is Steque, because it's exactly that data structure (but you need Empty as well, and it also deals with things other than A => B). The only issue in your suggestion is that you're missing a notion of "stack-safe value"; a value accompanied by functions which will be applied to it later. Adding that in makes it equivalent to Free[Id, ?] if we implement Free using Steque.

johnynek · 2017-06-08T20:38:58Z

free/src/main/scala/cats/free/Coyoneda.scala

-  /** The transformer function, to be lifted into `F` by `run`. */
-  val k: Pivot => A
+  /** The transformer functions, to be lifted into `F` by `run`. */
+  private[cats] val k: List[Any => Any]


what if we called this ks and keep def k: Pivot => A = execute _ so we don't break binary compatibility here?

👍 Done, got it down as final def k and added a doc.

johnynek · 2017-06-08T20:39:43Z

free/src/main/scala/cats/free/Coyoneda.scala


  /** Converts to `Yoneda[F,A]` given that `F` is a functor */
  final def toYoneda(implicit F: Functor[F]): Yoneda[F, A] =
    new Yoneda[F, A] {
-      def apply[B](f: A => B): F[B] = F.map(fi)(k andThen f)
+      def apply[B](f: A => B): F[B] = F.map(fi)(execute _ andThen f)


if we keep k we can not change this line.

johnynek · 2017-06-12T01:17:49Z

👍

kailuowang · 2017-06-12T15:08:29Z

merging with 3 sign-offs

stew added the in progress label Apr 12, 2017

edmundnoble added Source Breaking Binary Breaking and removed in progress labels Apr 12, 2017

adelbertc reviewed Apr 12, 2017

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edmundnoble force-pushed the coyo-stack-safe branch from 283877a to 5e82854 Compare April 12, 2017 05:15

edmundnoble force-pushed the coyo-stack-safe branch from 5e82854 to 29e23ea Compare April 12, 2017 06:23

kailuowang added this to the 1.0.0-MF milestone Apr 12, 2017

wedens reviewed Apr 12, 2017

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edmundnoble force-pushed the coyo-stack-safe branch from 29e23ea to 8d6073e Compare April 13, 2017 04:45

kailuowang reviewed Apr 13, 2017

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kailuowang mentioned this pull request May 25, 2017

Prepare for the 1.0.0-MF release #1702

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kailuowang approved these changes Jun 8, 2017

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adelbertc approved these changes Jun 8, 2017

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johnynek reviewed Jun 8, 2017

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Stack-safe Coyoneda

19c6561

edmundnoble force-pushed the coyo-stack-safe branch from 8d6073e to 19c6561 Compare June 11, 2017 21:36

kailuowang merged commit 1ffaeae into typelevel:master Jun 12, 2017

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Stack-safe Coyoneda #1602

Stack-safe Coyoneda #1602

edmundnoble commented Apr 12, 2017

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Stack-safe Coyoneda #1602

Stack-safe Coyoneda #1602

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