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Add Foldable extension collectFirstSomeM #2366

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merged 4 commits into from
Aug 15, 2018
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Add Foldable extension collectFirstSomeM #2366

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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
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catostrophe Aug 11, 2018
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11 changes: 6 additions & 5 deletions core/src/main/scala/cats/syntax/foldable.scala
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Original file line number Diff line number Diff line change
@@ -1,8 +1,6 @@
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 @@ -116,7 +114,10 @@ final class FoldableOps[F[_], A](val fa: F[A]) extends AnyVal {
* }}}
*/
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) =>
Eval.now(OptionT(f(a)).orElse(lb.value))
).value.value
F.foldRight(fa, Eval.now(G.pure(Option.empty[B])))((a, lb) =>
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👍

Eval.now(G.flatMap(f(a)) {
case s @ Some(_) => G.pure(s)
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We could also match on None first and then add case s - we'll avoid an instance check and cast, so it could be good for performance. Not sure if the difference is significant though, we'd need to benchmark. Feel free to ignore this comment ;)

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Got it. Let me perform some jmh benchmarks.

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@kubukoz JMH proved you right :)

case None => lb.value
})
).value
}