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add more doctest to WriterT #3073

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Oct 5, 2019
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add more doctest to WriterT #3073

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235 changes: 235 additions & 0 deletions core/src/main/scala/cats/data/WriterT.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -7,39 +7,152 @@ import cats.kernel.CommutativeMonoid
import cats.syntax.semigroup._

final case class WriterT[F[_], L, V](run: F[(L, V)]) {

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, List[String], Int](Some(123))
* scala> writer.tell(List("a","b","c")).tell(List("d","e","f"))
* res0: WriterT[Option, List[String], Int] = WriterT(Some((List(a, b, c, d, e, f),123)))
* }}}
*/
def tell(l: L)(implicit functorF: Functor[F], semigroupL: Semigroup[L]): WriterT[F, L, V] =
mapWritten(_ |+| l)

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer: WriterT[Option, List[String], Int] = WriterT.liftF(Some(123))
* scala> writer.tell(List("a","b","c")).written.getOrElse(Nil)
* res0: List[String] = List(a, b, c)
* }}}
*/
def written(implicit functorF: Functor[F]): F[L] =
functorF.map(run)(_._1)

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer: WriterT[Option, List[String], Int] = WriterT.liftF(Some(123))
* scala> val wt: WriterT[Option, List[String], Int] = writer.tell(List("error"))
* res0: WriterT[Option, List[String], Int] = WriterT(Some((List(error),123)))
*
* scala> wt.value
* res1: Option[Int] = Some(123)
* }}}
*/
def value(implicit functorF: Functor[F]): F[V] =
functorF.map(run)(_._2)

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer: WriterT[Option, String, Int] = WriterT.liftF(Some(123))
* scala> val wt: WriterT[Option, String, Int] = writer.tell("error").tell(" log")
* res0: WriterT[Option, String, Int] = WriterT(Some((error log,123)))
*
* scala> wt.listen
* res1: WriterT[Option, String, (Int,String)] = WriterT(Some((error log,(123,error log))))
* }}}
*/
def listen(implicit F: Functor[F]): WriterT[F, L, (V, L)] =
WriterT(F.map(run) {
case (l, v) => (l, (v, l))
})

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer: WriterT[Option, String, Int] = WriterT.liftF(Some(123))
* scala> val wt: WriterT[Option, String, Int] = writer.tell("error")
* res0: WriterT[Option, String, Int] = WriterT(Some((error,123)))
*
* scala> val func = WriterT.liftF[Option, String, Int => List[Int]](Some(i => List(i)))
* scala> val func2 = func.tell("log")
*
* scala> wt.ap(func2)
* res1: WriterT[Option, String, List[Int]] = WriterT(Some((logerror,List(123))))
* }}}
*/
def ap[Z](f: WriterT[F, L, V => Z])(implicit F: Apply[F], L: Semigroup[L]): WriterT[F, L, Z] =
WriterT(F.map2(f.run, run) {
case ((l1, fvz), (l2, v)) => (L.combine(l1, l2), fvz(v))
})

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val wr1: WriterT[Option, String, Int] = WriterT.liftF(None)
* scala> val wr2 = wr1.tell("error")
* res0: WriterT[Option, String, Int] = WriterT(None)
*
* scala> wr2.map(_ * 2)
* res1: WriterT[Option, String, Int] = WriterT(None)
*
* scala> val wr3: WriterT[Option, String, Int] = WriterT.liftF(Some(456))
* scala> val wr4 = wr3.tell("error")
* scala> wr4.map(_ * 2)
* res2: WriterT[Option, String, Int] = WriterT(Some((error,912)))
* }}}
*/
def map[Z](fn: V => Z)(implicit functorF: Functor[F]): WriterT[F, L, Z] =
WriterT {
functorF.map(run) { z =>
(z._1, fn(z._2))
}
}

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val wr1: WriterT[Option, String, Int] = WriterT.liftF(Some(123))
* scala> val wr2 = wr1.tell("log...")
* scala> wr2.imap(_ * 2)(_ / 2)
* res0: WriterT[Option, String, Int] = WriterT(Some((log...,246)))
* }}}
*/
def imap[Z](f: V => Z)(g: Z => V)(implicit F: Invariant[F]): WriterT[F, L, Z] =
WriterT {
F.imap(run)(z => (z._1, f(z._2)))(z => (z._1, g(z._2)))
}

/**
* Modify the context `F` using transformation `f`.
*
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.arrow.FunctionK
* scala> import cats.implicits._
*
* scala> val optionWriter = WriterT.liftF[Option, String, Int](Some(123)).tell("log")
* res0: WriterT[Option, String, Int](Some((log,123)))
*
* scala> def toList[A](option: Option[A]): List[A] = option.toList
* scala> val listWriter = optionWriter.mapK(FunctionK.lift(toList _))
* res1: WriterT[List, String, Int](List((log,123)))
* }}}
*/
def mapK[G[_]](f: F ~> G): WriterT[G, L, V] =
WriterT[G, L, V](f(run))
Expand All @@ -51,6 +164,20 @@ final case class WriterT[F[_], L, V](run: F[(L, V)]) {
}
}

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val wr1 = WriterT.liftF[Option, String, Int](Some(123)).tell("error")
* res0: WriterT[Option, String, Int] = WriterT(Some(error,123))
* scala> val func = (i:Int) => WriterT.liftF[Option, String, Int](Some(i * 2)).tell(i.show)
*
* scala> wr1.flatMap(func)
* res1: WriterT[Option, String, Int] = WriterT(Some((error123,246)))
* }}}
*/
def flatMap[U](f: V => WriterT[F, L, U])(implicit flatMapF: FlatMap[F], semigroupL: Semigroup[L]): WriterT[F, L, U] =
WriterT {
flatMapF.flatMap(run) { lv =>
Expand All @@ -60,29 +187,137 @@ final case class WriterT[F[_], L, V](run: F[(L, V)]) {
}
}

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val wr1 = WriterT.liftF[Option, String, Int](Some(123)).tell("quack")
* res0: WriterT[Option, String, Int] = WriterT(Some(quack,123))
*
* scala> wr1.mapBoth((s,i) => (s + " " + s, i * 2))
* res1: WriterT[Option, String, Int] = WriterT(Some((quack quack,246)))
* }}}
*/
def mapBoth[M, U](f: (L, V) => (M, U))(implicit functorF: Functor[F]): WriterT[F, M, U] =
WriterT { functorF.map(run)(f.tupled) }

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val wr1 = WriterT.liftF[Option, String, Int](Some(123)).tell("456")
* res0: WriterT[Option, String, Int] = WriterT(Some(456,123))
*
* scala> wr1.bimap(_.toInt, _.show)
* res1: WriterT[Option, Int, String] = WriterT(Some((456,123)))
* }}}
*/
def bimap[M, U](f: L => M, g: V => U)(implicit functorF: Functor[F]): WriterT[F, M, U] =
mapBoth((l, v) => (f(l), g(v)))

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(246)).tell("error")
* res0: WriterT[Option, String, Int] = WriterT(Some((error,246)))
*
* scala> writer.mapWritten(i => List(i))
* res1: WriterT[Option, List[String], Int] = WriterT(Some((List(error),246)))
* }}}
*/
def mapWritten[M](f: L => M)(implicit functorF: Functor[F]): WriterT[F, M, V] =
mapBoth((l, v) => (f(l), v))

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(123)).tell("log")
* scala> writer.swap
* res0: WriterT[Option, Int, String] = WriterT(Some((123,log)))
* }}}
*/
def swap(implicit functorF: Functor[F]): WriterT[F, V, L] =
mapBoth((l, v) => (v, l))

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(123)).tell("error")
* scala> writer.reset
* res0: WriterT[Option, String, Int] = WriterT(Some((,123)))
* }}}
*/
def reset(implicit monoidL: Monoid[L], functorF: Functor[F]): WriterT[F, L, V] =
mapWritten(_ => monoidL.empty)

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(456)).tell("log...")
* scala> writer.show
* res0: String = Some((log...,456))
* }}}
*/
def show(implicit F: Show[F[(L, V)]]): String = F.show(run)

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(123)).tell("hi")
* scala> writer.foldLeft(456)((acc,v) => acc + v)
* res0: Int = 579
* }}}
*/
def foldLeft[C](c: C)(f: (C, V) => C)(implicit F: Foldable[F]): C =
F.foldLeft(run, c)((z, lv) => f(z, lv._2))

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.Eval
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(123)).tell("hi")
* scala> writer
* | .foldRight(Eval.now(456))((v,c) => c.map(_ + v))
* | .value
* res0: Int = 579
* }}}
*/
def foldRight[C](lc: Eval[C])(f: (V, Eval[C]) => Eval[C])(implicit F: Foldable[F]): Eval[C] =
F.foldRight(run, lc)((lv, z) => f(lv._2, z))

/**
* Example:
* {{{
* scala> import cats.data.WriterT
* scala> import cats.implicits._
*
* scala> val writer = WriterT.liftF[Option, String, Int](Some(123)).tell("hi")
* scala> writer.traverse[List,Int](i => List(i))
* res0: List[WriterT[Option, String, Int]] = List(WriterT(Some((hi,123))))
* }}}
*/
def traverse[G[_], V1](f: V => G[V1])(implicit F: Traverse[F], G: Applicative[G]): G[WriterT[F, L, V1]] =
G.map(
F.traverse(run)(lv => G.tupleLeft(f(lv._2), lv._1))
Expand Down