Implements foldMap in terms of foldRight
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- Dominant language
- Scala
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Description
A lazy foldMap permit to have a relatively efficiently headOption, all, exist ... e.g.
case class First[A](value: Option[A])
implicit def firstMonoidK[First] = new MonoidK[First]{
def empty[A] = First(None)
def combine[A](f1: First[A], f2: First[A]): First[A] =
First(f1.value orElse f2.value)
}
trait Foldable[F[_]]{
def headOption(fa: F[A]): Option[A] =
foldMap(fa)(a => First(Some(a)))
}
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start at the Foldable entry point and read the existing foldRight API. Compare the requested foldMap behavior with the headOption, all, and exist examples, paying attention to laziness. Done means Foldable supports the requested foldMap use cases without losing that laziness.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- scala
- Domain
- backend
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100