Optimize Iterable instances implementation.

alleycats-core/src/main/scala/alleycats/std/iterable.scala

@@ -15,5 +15,25 @@ trait IterableInstances {
 
       override def foldMap[A, B](fa: Iterable[A])(f: A => B)(implicit B: Monoid[B]): B =
         B.combineAll(fa.iterator.map(f))
+
+      override def reduceLeftOption[A](fa: Iterable[A])(f: (A, A) => A): Option[A] = fa.reduceLeftOption(f)
+
+      override def collectFirst[A, B](fa: Iterable[A])(pf: PartialFunction[A, B]): Option[B] = fa.collectFirst(pf)
+
+      override def fold[A](fa: Iterable[A])(implicit A: Monoid[A]): A = fa.fold(A.empty)(A.combine)
+
+      override def find[A](fa: Iterable[A])(f: A => Boolean): Option[A] = fa.find(f)
+
+      override def toIterable[A](fa: Iterable[A]): Iterable[A] = fa
+
+      override def exists[A](fa: Iterable[A])(p: A => Boolean): Boolean = fa.exists(p)
+
+      override def forall[A](fa: Iterable[A])(p: A => Boolean): Boolean = fa.forall(p)
+
+      override def toList[A](fa: Iterable[A]): List[A] = fa.toList
+
+      override def isEmpty[A](fa: Iterable[A]): Boolean = fa.isEmpty
+
+      override def nonEmpty[A](fa: Iterable[A]): Boolean = fa.nonEmpty
     }
 }

alleycats-tests/shared/src/test/scala/alleycats/tests/AlleycatsSuite.scala

@@ -6,12 +6,12 @@ import cats._
 import cats.instances.AllInstances
 import cats.syntax.{AllSyntax, EqOps}
 import cats.tests.StrictCatsEquality
-import org.scalatest.Matchers
 import org.scalatest.funsuite.AnyFunSuiteLike
 import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
 import org.typelevel.discipline.scalatest.Discipline
 import org.scalacheck.{Arbitrary, Gen}
 import org.scalacheck.Arbitrary.arbitrary
+import org.scalatest.matchers.should.Matchers
 
 import scala.util.{Failure, Success, Try}
 
@@ -36,6 +36,8 @@ trait AlleycatsSuite
   // disable Eq syntax (by making `catsSyntaxEq` not implicit), since it collides
   // with scalactic's equality
   override def catsSyntaxEq[A: Eq](a: A): EqOps[A] = new EqOps[A](a)
+
+  implicit def EqIterable[A: Eq]: Eq[Iterable[A]] = Eq.by(_.toList)
 }
 
 sealed trait TestInstances {

alleycats-tests/shared/src/test/scala/alleycats/tests/IterableTests.scala

@@ -3,6 +3,7 @@ package tests
 
 import cats.{Eval, Foldable}
 import alleycats.std.all._
+import cats.laws.discipline.FoldableTests
 
 class IterableTests extends AlleycatsSuite {
 
@@ -22,4 +23,5 @@ class IterableTests extends AlleycatsSuite {
       .value shouldEqual (Eval.now("OK").value)
   }
 
+  checkAll("Foldable[Iterable]", FoldableTests[Iterable].foldable[Int, Int])
 }