Add ifF on Functor #3040

core/src/main/scala/cats/Functor.scala

@@ -144,6 +144,20 @@ import simulacrum.typeclass
    */
   def tupleRight[A, B](fa: F[A], b: B): F[(A, B)] = map(fa)(a => (a, b))
 
+  /**
+   * Lifts `if` to Functor
+   *
+   * Example:
+   * {{{
+   * scala> import cats.Functor
+   * scala> import cats.implicits.catsStdInstancesForList
+   *
+   * scala> Functor[List].ifF(List(true, false, false))(1, 0)
+   * res0: List[Int] = List(1, 0, 0)
+   * }}}
+   */
+  def ifF[A](fb: F[Boolean])(ifTrue: => A, ifFalse: => A): F[A] = map(fb)(x => if (x) ifTrue else ifFalse)
+
   def compose[G[_]: Functor]: Functor[λ[α => F[G[α]]]] =
     new ComposedFunctor[F, G] {
       val F = self

tests/src/test/scala/cats/tests/FunctorSuite.scala

@@ -37,4 +37,21 @@ class FunctorSuite extends CatsSuite {
       assert(widened eq list)
     }
   }
+
+  test("ifF equals map(if(_) ifTrue else ifFalse)") {
+    forAll { (l: List[Boolean], o: Option[Boolean], m: Map[String, Boolean]) =>
+      Functor[List].ifF(l)(1, 0) should ===(l.map(if (_) 1 else 0))
+      Functor[Option].ifF(o)(1, 0) should ===(o.map(if (_) 1 else 0))
+    }
+  }
+
+  test("ifF equals map(if(_) ifTrue else ifFalse) for concrete lists and optoins") {
+    Functor[List].ifF(List(true, false, false, true))(1, 0) should ===(List(1, 0, 0, 1))
+    Functor[List].ifF(List.empty[Boolean])(1, 0) should ===(Nil)
+    Functor[Option].ifF(Some(true))(1, 0) should ===(Some(1))
+    Functor[Option].ifF(Some(false))(1, 0) should ===(Some(0))
+    Functor[Option].ifF(None)(1, 0) should ===(None)
+
+  }
+
 }