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Add StateT transformS #780
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Original file line number | Diff line number | Diff line change |
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@@ -73,6 +73,20 @@ final class StateT[F[_], S, A](val runF: F[S => F[(S, A)]]) extends Serializable | |
def transformF[G[_], B](f: F[(S, A)] => G[(S, B)])(implicit F: FlatMap[F], G: Applicative[G]): StateT[G, S, B] = | ||
StateT(s => f(run(s))) | ||
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/** Transform the state used | ||
* | ||
* This is useful when you are working with many focused `StateT`s and want to pass in a | ||
* global state containing the various states needed for each individual `StateT`. | ||
*/ | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Love it. |
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def transformS[R](f: R => S, g: (R, S) => R)(implicit F: Monad[F]): StateT[F, R, A] = | ||
StateT { r => | ||
F.flatMap(runF) { ff => | ||
val s = f(r) | ||
val nextState = ff(s) | ||
F.map(nextState) { case (s, a) => (g(r, s), a) } | ||
} | ||
} | ||
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/** | ||
* Modify the state (`S`) component. | ||
*/ | ||
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Unjustifiably nitpicky: could you bump "Transform..." down to the next line to be consistent with the other ScalaDoc comments?
Also, what do you think about adding an sbt-doctest example here?