Added collectFirst to Chain and NonEmptyChain

core/src/main/scala/cats/data/Chain.scala

@@ -145,6 +145,39 @@ sealed abstract class Chain[+A] {
       else acc
     }
 
+  /**
+   * Finds the first element of this `Chain` for which the given partial
+   * function is defined, and applies the partial function to it.
+   */
+  final def collectFirst[B](pf: PartialFunction[A, B]): Option[B] = {
+    var result: Option[B] = None
+    foreachUntil { a =>
+      // trick from TraversableOnce, used to avoid calling both isDefined and apply (or calling lift)
+      val x = pf.applyOrElse(a, sentinel)
+      if (x.asInstanceOf[AnyRef] ne sentinel) {
+        result = Some(x.asInstanceOf[B])
+        true
+      } else false
+    }
+    result
+  }
+
+  /**
+   * Like `collectFirst` from `scala.collection.Traversable` but takes `A => Option[B]`
+   * instead of `PartialFunction`s.
+   */
+  final def collectFirstSome[B](f: A => Option[B]): Option[B] = {
+    var result: Option[B] = None
+    foreachUntil { a =>
+      val x = f(a)
+      if (x.isDefined) {
+        result = x
+        true
+      } else false
+    }
+    result
+  }
+
   /**
    * Remove elements not matching the predicate
    */
@@ -560,6 +593,8 @@ sealed abstract private[data] class ChainInstances extends ChainInstances1 {
       override def forall[A](fa: Chain[A])(p: A => Boolean): Boolean = fa.forall(p)
       override def find[A](fa: Chain[A])(f: A => Boolean): Option[A] = fa.find(f)
       override def size[A](fa: Chain[A]): Long = fa.length
+      override def collectFirst[A, B](fa: Chain[A])(pf: PartialFunction[A, B]): Option[B] = fa.collectFirst(pf)
+      override def collectFirstSome[A, B](fa: Chain[A])(f: A => Option[B]): Option[B] = fa.collectFirstSome(f)
 
       def coflatMap[A, B](fa: Chain[A])(f: Chain[A] => B): Chain[B] = {
         @tailrec def go(as: Chain[A], res: ListBuffer[B]): Chain[B] =

core/src/main/scala/cats/data/NonEmptyChain.scala

@@ -239,6 +239,18 @@ class NonEmptyChainOps[A](private val value: NonEmptyChain[A]) extends AnyVal {
    */
   final def collect[B](pf: PartialFunction[A, B]): Chain[B] = toChain.collect(pf)
 
+  /**
+   * Finds the first element of this `NonEmptyChain` for which the given partial
+   * function is defined, and applies the partial function to it.
+   */
+  final def collectFirst[B](pf: PartialFunction[A, B]): Option[B] = toChain.collectFirst(pf)
+
+  /**
+   * Like `collectFirst` from `scala.collection.Traversable` but takes `A => Option[B]`
+   * instead of `PartialFunction`s.
+   */
+  final def collectFirstSome[B](f: A => Option[B]): Option[B] = toChain.collectFirstSome(f)
+
   /**
    * Filters all elements of this chain that do not satisfy the given predicate.
    */
@@ -473,6 +485,12 @@ sealed abstract private[data] class NonEmptyChainInstances extends NonEmptyChain
 
       override def toNonEmptyList[A](fa: NonEmptyChain[A]): NonEmptyList[A] =
         fa.toNonEmptyList
+
+      override def collectFirst[A, B](fa: NonEmptyChain[A])(pf: PartialFunction[A, B]): Option[B] =
+        fa.collectFirst(pf)
+
+      override def collectFirstSome[A, B](fa: NonEmptyChain[A])(f: A => Option[B]): Option[B] =
+        fa.collectFirstSome(f)
     }
 
   implicit def catsDataOrderForNonEmptyChain[A: Order]: Order[NonEmptyChain[A]] =