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Add state method to MonadState #1651

Merged
merged 5 commits into from
May 10, 2017
Merged

Add state method to MonadState #1651

merged 5 commits into from
May 10, 2017

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oskoi
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@oskoi oskoi commented May 6, 2017

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edmundnoble
edmundnoble suggested changes May 6, 2017
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a) apply on a trait is a recipe for name collisions. Call it state maybe, to be consistent with reader on MonadReader?
b) It's not consistent to have this on MonadState and have no method from Either on MonadError.

@oskoi
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oskoi commented May 7, 2017 •
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@edmundnoble
a) You're right. Changed the name of method.
b) Sorry, but I did not understand you. We have method raiseError in MonadError. Explain, please, what did you mean

@oskoi oskoi changed the title Add apply method to MonadState Add state method to MonadState May 7, 2017
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To clarify and correct myself, in ApplicativeError, a method def either[A](x: E Either A): F[A], which just calls _.fold(raiseError, pure).

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oskoi commented May 7, 2017

@edmundnoble done.

edmundnoble
edmundnoble approved these changes May 7, 2017
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LGTM.

peterneyens
peterneyens reviewed May 8, 2017
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core/src/main/scala/cats/MonadState.scala Outdated
@@ -17,6 +17,9 @@ package cats
* }}}
*/
trait MonadState[F[_], S] extends Monad[F] {
def state[A](f: S => (S, A)): F[A] =
flatMap(get)(s => f(s) match { case (s, a) => inspect(_ => a)})
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Shouldn't this use set to set the S resulting from f(s)? As is this will just return the initial S, right?

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@peterneyens Right. Forgot to update the state ( Fixed this!

@kailuowang
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We might want to add some doctests.

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oskoi commented May 8, 2017

@kailuowang done

kailuowang
kailuowang approved these changes May 8, 2017
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LGTM

@edmundnoble edmundnoble merged commit 8c38980 into typelevel:master May 10, 2017
@peterneyens peterneyens mentioned this pull request May 11, 2017
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@kailuowang kailuowang modified the milestone: 1.0.0-MF May 18, 2017
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@peterneyens peterneyens peterneyens left review comments

@kailuowang kailuowang kailuowang approved these changes

@edmundnoble edmundnoble edmundnoble approved these changes

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@oskoi @edmundnoble @kailuowang @peterneyens