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Add state method to MonadState #1651

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merged 5 commits into from
May 10, 2017
Merged

Add state method to MonadState #1651

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14db779
Add apply method to MonadState
May 6, 2017
1c24e5b
Rename apply method to state
May 7, 2017
5e82dd4
Add fromEither
May 7, 2017
304b2f6
Add updating new state
May 8, 2017
d4386b5
Add doctests
May 8, 2017
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6 changes: 6 additions & 0 deletions core/src/main/scala/cats/ApplicativeError.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,12 @@ trait ApplicativeError[F[_], E] extends Applicative[F] {
case Success(a) => pure(a)
case Failure(e) => raiseError(e)
}

/**
* Convert from scala.Either
*/
def fromEither[A](x: E Either A): F[A] =
x.fold(raiseError, pure)
}

object ApplicativeError {
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3 changes: 3 additions & 0 deletions core/src/main/scala/cats/MonadState.scala
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Expand Up @@ -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!


def get: F[S]

def set(s: S): F[Unit]
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