Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Add Foldable extension collectFirstSomeM #2366

Merged
merged 4 commits into from
Aug 15, 2018
Merged

Add Foldable extension collectFirstSomeM #2366

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
743f0f9
Add Foldable extension collectFirstSomeM
catostrophe Aug 11, 2018
b45aa14
Implement without OptionT
catostrophe Aug 11, 2018
6af9ee4
Optimize pattern matching
catostrophe Aug 11, 2018
8b8024a
Empty commit
catostrophe Aug 11, 2018
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
27 changes: 27 additions & 0 deletions core/src/main/scala/cats/syntax/foldable.scala
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
package cats
package syntax

import cats.data.OptionT

trait FoldableSyntax extends Foldable.ToFoldableOps with UnorderedFoldable.ToUnorderedFoldableOps {
implicit final def catsSyntaxNestedFoldable[F[_]: Foldable, G[_], A](fga: F[G[A]]): NestedFoldableOps[F, G, A] =
new NestedFoldableOps[F, G, A](fga)
Expand Down Expand Up @@ -92,4 +94,29 @@ final class FoldableOps[F[_], A](val fa: F[A]) extends AnyVal {
b.toString.dropRight(delim.length)
} + suffix
}

/**
* Monadic version of `collectFirstSome`.
* {{{
* scala> import cats.implicits._
* scala> def parseInt(s: String): Either[String, Int] = Either.catchOnly[NumberFormatException](s.toInt).leftMap(_.getMessage)
* scala> val keys1 = List("1", "2", "4", "5")
* scala> val map1 = Map(4 -> "Four", 5 -> "Five")
* scala> keys1.collectFirstSomeM(parseInt(_) map map1.get)
* res1: scala.util.Either[String,Option[String]] = Right(Some(Four))
* scala> val map2 = Map(6 -> "Six", 7 -> "Seven")
* scala> keys1.collectFirstSomeM(parseInt(_) map map2.get)
* res2: scala.util.Either[String,Option[String]] = Right(None)
* scala> val keys2 = List("1", "x", "4", "5")
* scala> keys2.collectFirstSomeM(parseInt(_) map map1.get)
* res3: scala.util.Either[String,Option[String]] = Left(For input string: "x")
* scala> val keys3 = List("1", "2", "4", "x")
* scala> keys3.collectFirstSomeM(parseInt(_) map map1.get)
* res4: scala.util.Either[String,Option[String]] = Right(Some(Four))
* }}}
*/
def collectFirstSomeM[G[_], B](f: A => G[Option[B]])(implicit F: Foldable[F], G: Monad[G]): G[Option[B]] =
F.foldRight(fa, Eval.now(OptionT.none[G, B]))((a, lb) =>
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Would it be possible to implement this without OptionT? I think there's some overhead involved when wrapping values in monad transformers, and this is library code so it shouldn't be that problematic to use the wrapped values directly

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sure, it would. Will do if you think it's worth it.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yeah let's try to do it as efficiently as possible :)

Eval.now(OptionT(f(a)).orElse(lb.value))
).value.value
}
10 changes: 9 additions & 1 deletion tests/src/test/scala/cats/tests/FoldableSuite.scala
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -140,12 +140,20 @@ abstract class FoldableSuite[F[_]: Foldable](name: String)(
fa.toList should === (iterator(fa).toList)
}
}

test(s"Foldable[$name] mkString_") {
forAll { (fa: F[Int]) =>
fa.mkString_("L[", ";", "]") should === (fa.toList.mkString("L[", ";", "]"))
}
}

test(s"Foldable[$name].collectFirstSomeM") {
forAll { (fa: F[Int], n: Int) =>
fa.collectFirstSomeM(x => (x > n).guard[Option].as(x).asRight[String]) should === (fa.toList.collectFirst {
case x if x > n => x
}.asRight[String])
}
}
}

class FoldableSuiteAdditional extends CatsSuite {
Expand Down