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Add doctest examples for Apply #2086

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Dec 19, 2017
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Add doctest examples for Apply #2086

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5e050ac
Add doctest examples for Apply
ceedubs Dec 9, 2017
8f92f06
Merge branch 'master' into apply-doctest
ceedubs Dec 18, 2017
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122 changes: 120 additions & 2 deletions core/src/main/scala/cats/Apply.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -14,14 +14,97 @@ trait Apply[F[_]] extends Functor[F] with Semigroupal[F] with ApplyArityFunction
/**
* Given a value and a function in the Apply context, applies the
* function to the value.
*
* Example:
* {{{
* scala> import cats.implicits._
*
* scala> val someF: Option[Int => Long] = Some(_.toLong + 1L)
* scala> val noneF: Option[Int => Long] = None
* scala> val someInt: Option[Int] = Some(3)
* scala> val noneInt: Option[Int] = None
*
* scala> Apply[Option].ap(someF)(someInt)
* res0: Option[Long] = Some(4)
*
* scala> Apply[Option].ap(noneF)(someInt)
* res1: Option[Long] = None
*
* scala> Apply[Option].ap(someF)(noneInt)
* res2: Option[Long] = None
*
* scala> Apply[Option].ap(noneF)(noneInt)
* res3: Option[Long] = None
* }}}
*/
def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]

/** Compose two actions, discarding any value produced by the first. */
/**
* Compose two actions, discarding any value produced by the first.
*
* @see [[productL]] to discard the value of the second instead.
*
* Example:
* {{{
* scala> import cats.implicits._
* scala> import cats.data.Validated
* scala> import Validated.{Valid, Invalid}
*
* scala> type ErrOr[A] = Validated[String, A]
*
* scala> val validInt: ErrOr[Int] = Valid(3)
* scala> val validBool: ErrOr[Boolean] = Valid(true)
* scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.")
* scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.")
*
* scala> Apply[ErrOr].productR(validInt)(validBool)
* res0: ErrOr[Boolean] = Valid(true)
*
* scala> Apply[ErrOr].productR(invalidInt)(validBool)
* res1: ErrOr[Boolean] = Invalid(Invalid int.)
*
* scala> Apply[ErrOr].productR(validInt)(invalidBool)
* res2: ErrOr[Boolean] = Invalid(Invalid boolean.)
*
* scala> Apply[ErrOr].productR(invalidInt)(invalidBool)
* res3: ErrOr[Boolean] = Invalid(Invalid int.Invalid boolean.)
* }}}
*
*/
def productR[A, B](fa: F[A])(fb: F[B]): F[B] =
map2(fa, fb)((_, b) => b)

/** Compose two actions, discarding any value produced by the second. */
/**
* Compose two actions, discarding any value produced by the second.
*
* @see [[productR]] to discard the value of the first instead.
*
* Example:
* {{{
* scala> import cats.implicits._
* scala> import cats.data.Validated
* scala> import Validated.{Valid, Invalid}
*
* scala> type ErrOr[A] = Validated[String, A]
*
* scala> val validInt: ErrOr[Int] = Valid(3)
* scala> val validBool: ErrOr[Boolean] = Valid(true)
* scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.")
* scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.")
*
* scala> Apply[ErrOr].productL(validInt)(validBool)
* res0: ErrOr[Int] = Valid(3)
*
* scala> Apply[ErrOr].productL(invalidInt)(validBool)
* res1: ErrOr[Int] = Invalid(Invalid int.)
*
* scala> Apply[ErrOr].productL(validInt)(invalidBool)
* res2: ErrOr[Int] = Invalid(Invalid boolean.)
*
* scala> Apply[ErrOr].productL(invalidInt)(invalidBool)
* res3: ErrOr[Int] = Invalid(Invalid int.Invalid boolean.)
* }}}
*/
def productL[A, B](fa: F[A])(fb: F[B]): F[A] =
map2(fa, fb)((a, _) => a)

Expand Down Expand Up @@ -60,6 +143,28 @@ trait Apply[F[_]] extends Functor[F] with Semigroupal[F] with ApplyArityFunction
* Applies the pure (binary) function f to the effectful values fa and fb.
*
* map2 can be seen as a binary version of [[cats.Functor]]#map.
*
* Example:
* {{{
* scala> import cats.implicits._
*
* scala> val someInt: Option[Int] = Some(3)
* scala> val noneInt: Option[Int] = None
* scala> val someLong: Option[Long] = Some(4L)
* scala> val noneLong: Option[Long] = None
*
* scala> Apply[Option].map2(someInt, someLong)((i, l) => i.toString + l.toString)
* res0: Option[String] = Some(34)
*
* scala> Apply[Option].map2(someInt, noneLong)((i, l) => i.toString + l.toString)
* res0: Option[String] = None
*
* scala> Apply[Option].map2(noneInt, noneLong)((i, l) => i.toString + l.toString)
* res0: Option[String] = None
*
* scala> Apply[Option].map2(noneInt, someLong)((i, l) => i.toString + l.toString)
* res0: Option[String] = None
* }}}
*/
def map2[A, B, Z](fa: F[A], fb: F[B])(f: (A, B) => Z): F[Z] =
map(product(fa, fb))(f.tupled)
Expand Down Expand Up @@ -89,6 +194,19 @@ trait Apply[F[_]] extends Functor[F] with Semigroupal[F] with ApplyArityFunction
def map2Eval[A, B, Z](fa: F[A], fb: Eval[F[B]])(f: (A, B) => Z): Eval[F[Z]] =
fb.map(fb => map2(fa, fb)(f))

/**
* Compose an `Apply[F]` and an `Apply[G]` into an `Apply[λ[α => F[G[α]]]]`.
*
* Example:
* {{{
* scala> import cats.implicits._
*
* scala> val alo = Apply[List].compose[Option]
*
* scala> alo.product(List(None, Some(true), Some(false)), List(Some(2), None))
* res1: List[Option[(Boolean, Int)]] = List(None, None, Some((true,2)), None, Some((false,2)), None)
* }}}
*/
def compose[G[_]: Apply]: Apply[λ[α => F[G[α]]]] =
new ComposedApply[F, G] {
val F = self
Expand Down