FoldableOps

Monadic version of collectFirstSome.

If there are no elements, the result is None. collectFirstSomeM short-circuits, i.e. once a Some element is found, no further effects are produced.

For example:

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)
res0: scala.util.Either[String,Option[String]] = Right(Some(Four))

scala> val map2 = Map(6 -> "Six", 7 -> "Seven")
scala> keys1.collectFirstSomeM(parseInt(_) map map2.get)
res1: scala.util.Either[String,Option[String]] = Right(None)

scala> val keys2 = List("1", "x", "4", "5")
scala> keys2.collectFirstSomeM(parseInt(_) map map1.get)
res2: 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)
res3: scala.util.Either[String,Option[String]] = Right(Some(Four))

Tear down a subset of this structure using a PartialFunction.

scala> import cats.implicits._
scala> val xs = List(1, 2, 3, 4)
scala> xs.collectFold { case n if n % 2 == 0 => n }
res0: Int = 6

test if F[A] contains an A, named contains_ to avoid conflict with existing contains which uses universal equality

Example:

scala> import cats.implicits._

scala> val l: List[Int] = List(1, 2, 3, 4)
scala> l.contains_(1)
res0: Boolean = true
scala> l.contains_(5)
res1: Boolean = false

Find the first element matching the effectful predicate, if one exists.

If there are no elements, the result is None. findM short-circuits, i.e. once an element is found, no further effects are produced.

For example:

scala> import cats.implicits._
scala> val list = List(1,2,3,4)
scala> list.findM(n => (n >= 2).asRight[String])
res0: Either[String,Option[Int]] = Right(Some(2))

scala> list.findM(n => (n > 4).asRight[String])
res1: Either[String,Option[Int]] = Right(None)

scala> list.findM(n => Either.cond(n < 3, n >= 2, "error"))
res2: Either[String,Option[Int]] = Right(Some(2))

scala> list.findM(n => Either.cond(n < 3, false, "error"))
res3: Either[String,Option[Int]] = Left(error)

Intercalate with a prefix and a suffix

Example:

scala> import cats.implicits._

scala> val l: List[String] = List("1", "2", "3")
scala> l.foldSmash("List(", ",", ")")
res0: String = List(1,2,3)

Make a string using Show, prefix, delimiter, and suffix.

Named as mkString_ to avoid conflict.

Example:

scala> import cats.implicits._

scala> val l: List[Int] = List(1, 2, 3)
scala> l.mkString_("L[", ";", "]")
res0: String = L[1;2;3]
scala> val el: List[Int] = List()
scala> el.mkString_("L[", ";", "]")
res1: String = L[]

Tear down a subset of this structure using a A => Option[M].

scala> import cats.implicits._
scala> val xs = List(1, 2, 3, 4)
scala> def f(n: Int): Option[Int] = if (n % 2 == 0) Some(n) else None
scala> xs.collectFoldSome(f)
res0: Int = 6