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Add foldF, cataF and emptyflatTap to OptionT #3335

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merged 9 commits into from
May 13, 2020
Merged

Add foldF, cataF and emptyflatTap to OptionT #3335

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12551ca
Add foldF, cataF and emptyflatMap to OptionT
Feb 29, 2020
a48ed5a
Make emptyflatTap more tolerant on type
Feb 29, 2020
69c0f01
Rename emptyflatTap to flatTapNone, fix docs
Feb 29, 2020
3dfd6bb
Add tests for new OptionT methods
Feb 29, 2020
6fa9007
Add OptionT.semiflatTap
ybasket Mar 10, 2020
ff699db
Merge branch 'master' into more-utils-for-optiont
ybasket Mar 12, 2020
f5d0419
fix formatting in OptionTSuite
ybasket Mar 12, 2020
e3f83ab
Merge remote-tracking branch 'upstream/master' into more-utils-for-op…
Apr 11, 2020
468e4f7
Rename OptionT.flatTapNone's argument for clarity
Apr 11, 2020
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30 changes: 30 additions & 0 deletions core/src/main/scala/cats/data/OptionT.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,21 @@ final case class OptionT[F[_], A](value: F[Option[A]]) {
def fold[B](default: => B)(f: A => B)(implicit F: Functor[F]): F[B] =
F.map(value)(_.fold(default)(f))

/** Transform this `OptionT[F, A]` into a `F[C]`.
*
* Example:
* {{{
* scala> import cats.implicits._
* scala> import cats.data.OptionT
*
* scala> val optionT: OptionT[List, Int] = OptionT[List, Int](List(Some(23), None))
* scala> optionT.foldF(Nil)(v => List(v, v * 2))
* res0: List[Int] = List(23, 46)
* }}}
*/
def foldF[B](default: => F[B])(f: A => F[B])(implicit F: FlatMap[F]): F[B] =
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@diesalbla diesalbla Apr 11, 2020 •
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Suggested change
def foldF[B](default: => F[B])(f: A => F[B])(implicit F: FlatMap[F]): F[B] =
def foldF[B](ifNone: => F[B])(withSome: A => F[B])(implicit F: FlatMap[F]): F[B] =

Should we add more informative names?

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While I agree with your intention (and have hence changed it on flatTapNone – thx), I would value consistency with fold more and keep the parameter names the same.

F.flatMap(value)(_.fold(default)(f))

/**
* Catamorphism on the Option. This is identical to [[fold]], but it only has
* one parameter list, which can result in better type inference in some
Expand All @@ -24,6 +39,14 @@ final case class OptionT[F[_], A](value: F[Option[A]]) {
def cata[B](default: => B, f: A => B)(implicit F: Functor[F]): F[B] =
fold(default)(f)

/**
* Effectful catamorphism on the Option. This is identical to [[foldF]], but it only has
* one parameter list, which can result in better type inference in some
* contexts.
*/
def cataF[B](default: => F[B], f: A => F[B])(implicit F: FlatMap[F]): F[B] =
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I am aware of the notions of catamorphisms, but is that also a unified term or notion across cats? I can only grep the words def cata in OptionTand in CoFree.

Unless we want to extend the use across the whole of cats, perhaps we should drop them, to avoid confusion.

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There's a cata to fold already, so when seeing foldF, I'd expect cataF there as well. Whether cata should have been introduced with that name in the first place seems to be outside of the scope of this PR…but that's just my two cents.

foldF(default)(f)

def map[B](f: A => B)(implicit F: Functor[F]): OptionT[F, B] =
OptionT(F.map(value)(_.map(f)))

Expand Down Expand Up @@ -63,6 +86,13 @@ final case class OptionT[F[_], A](value: F[Option[A]]) {
def subflatMap[B](f: A => Option[B])(implicit F: Functor[F]): OptionT[F, B] =
transform(_.flatMap(f))

/**
* Perform an effect if the value inside the is a [[None]], leaving the result untouched. Equivalent to [[orElseF]]
* with an effect returning [[None]] as argument.
*/
def emptyflatTap[B](f: => F[B])(implicit F: Monad[F]): OptionT[F, A] =
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OptionT(F.flatTap(value)(_.fold(F.void(f))(_ => F.unit)))

def getOrElse[B >: A](default: => B)(implicit F: Functor[F]): F[B] =
F.map(value)(_.getOrElse(default))

Expand Down