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Adding reader method to MonadReader #1391

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Sep 22, 2016
Merged

Adding reader method to MonadReader #1391

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3 changes: 3 additions & 0 deletions core/src/main/scala/cats/MonadReader.scala
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Expand Up @@ -7,6 +7,9 @@ trait MonadReader[F[_], R] extends Monad[F] {

/** Modify the environment */
def local[A](f: R => R)(fa: F[A]): F[A]

/** Retrieves a function of the environment */
def reader[A](f: R => A): F[A] = map(ask)(f)
}

object MonadReader {
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3 changes: 3 additions & 0 deletions laws/src/main/scala/cats/laws/MonadReaderLaws.scala
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Expand Up @@ -16,6 +16,9 @@ trait MonadReaderLaws[F[_], R] extends MonadLaws[F] {

def monadReaderLocalFlatMap[A, B](fra: F[A], f: A => F[B], g: R => R): IsEq[F[B]] =
F.local(g)(F.flatMap(fra)(f)) <-> F.flatMap(F.local(g)(fra))(a => F.local(g)(f(a)))

def monadReaderReaderAsk[A](f: R => A): IsEq[F[A]] =
F.reader(f) <-> F.map(F.ask)(f)
}

object MonadReaderLaws {
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3 changes: 2 additions & 1 deletion laws/src/main/scala/cats/laws/discipline/MonadReaderTests.scala
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Expand Up @@ -36,7 +36,8 @@ trait MonadReaderTests[F[_], R] extends MonadTests[F] {
"monadReader ask idempotent" -> laws.monadReaderAskIdempotent,
"monadReader local ask" -> forAll(laws.monadReaderLocalAsk _),
"monadReader local pure" -> forAll(laws.monadReaderLocalPure[A] _),
"monadReader local flatMap" -> forAll(laws.monadReaderLocalFlatMap[A, B] _)
"monadReader local flatMap" -> forAll(laws.monadReaderLocalFlatMap[A, B] _),
"monadReader reader ask" -> forAll(laws.monadReaderReaderAsk[A] _)
)
}
}
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