product and map can be implemented in terms of ap, fixes #904

core/src/main/scala/cats/Applicative.scala

@@ -29,6 +29,9 @@ import cats.std.list._
    */
   def pureEval[A](x: Eval[A]): F[A] = pure(x.value)
 
+  override def map[A, B](fa: F[A])(f: A => B): F[B] =
+    ap(pure(f))(fa)
+
   /**
     * Given `fa` and `n`, apply `fa` `n` times to construct an `F[List[A]]` value.
     */

core/src/main/scala/cats/Apply.scala

@@ -16,6 +16,9 @@ trait Apply[F[_]] extends Functor[F] with Cartesian[F] with ApplyArityFunctions[
    */
   def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]
 
+  override def product[A, B](fa: F[A], fb: F[B]): F[(A, B)] =
+    ap(map(fa)(a => (b: B) => (a, b)))(fb)
+
   /**
    * ap2 is a binary version of ap, defined in terms of ap.
    */
@@ -56,7 +59,6 @@ trait CompositeApply[F[_], G[_]]
   def ap[A, B](f: F[G[A => B]])(fa: F[G[A]]): F[G[B]] =
     F.ap(F.map(f)(gab => G.ap(gab)(_)))(fa)
 
-  def product[A, B](fa: F[G[A]], fb: F[G[B]]): F[G[(A, B)]] =
+  override def product[A, B](fa: F[G[A]], fb: F[G[B]]): F[G[(A, B)]] =
     F.map2(fa, fb)(G.product)
-
 }

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

@@ -98,10 +98,10 @@ private[data] sealed abstract class ConstInstances0 extends ConstInstances1 {
     def ap[A, B](f: Const[C, A => B])(fa: Const[C, A]): Const[C, B] =
       f.retag[B] combine fa.retag[B]
 
-    def map[A, B](fa: Const[C, A])(f: A => B): Const[C, B] =
+    override def map[A, B](fa: Const[C, A])(f: A => B): Const[C, B] =
       fa.retag[B]
 
-    def product[A, B](fa: Const[C, A], fb: Const[C, B]): Const[C, (A, B)] =
+    override def product[A, B](fa: Const[C, A], fb: Const[C, B]): Const[C, (A, B)] =
       fa.retag[(A, B)] combine fb.retag[(A, B)]
   }
 }
@@ -116,7 +116,7 @@ private[data] sealed abstract class ConstInstances1 {
     def ap[A, B](f: Const[C, A => B])(fa: Const[C, A]): Const[C, B] =
       fa.retag[B] combine f.retag[B]
 
-    def product[A, B](fa: Const[C, A], fb: Const[C, B]): Const[C, (A, B)] =
+    override def product[A, B](fa: Const[C, A], fb: Const[C, B]): Const[C, (A, B)] =
       fa.retag[(A, B)] combine fb.retag[(A, B)]
 
     def map[A, B](fa: Const[C, A])(f: A => B): Const[C, B] =

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

@@ -54,15 +54,15 @@ private[data] abstract class FuncInstances1 {
 
 sealed trait FuncFunctor[F[_], C] extends Functor[Lambda[X => Func[F, C, X]]] {
   def F: Functor[F]
-  def map[A, B](fa: Func[F, C, A])(f: A => B): Func[F, C, B] =
+  override def map[A, B](fa: Func[F, C, A])(f: A => B): Func[F, C, B] =
     fa.map(f)(F)
 }
 
 sealed trait FuncApply[F[_], C] extends Apply[Lambda[X => Func[F, C, X]]] with FuncFunctor[F, C] {
   def F: Apply[F]
   def ap[A, B](f: Func[F, C, A => B])(fa: Func[F, C, A]): Func[F, C, B] =
     Func.func(c => F.ap(f.run(c))(fa.run(c)))
-  def product[A, B](fa: Func[F, C, A], fb: Func[F, C, B]): Func[F, C, (A, B)] =
+  override def product[A, B](fa: Func[F, C, A], fb: Func[F, C, B]): Func[F, C, (A, B)] =
     Func.func(c => F.product(fa.run(c), fb.run(c)))
 }
 
@@ -121,11 +121,11 @@ private[data] abstract class AppFuncInstances {
 
 private[data] sealed trait AppFuncApplicative[F[_], C] extends Applicative[Lambda[X => AppFunc[F, C, X]]] {
   def F: Applicative[F]
-  def map[A, B](fa: AppFunc[F, C, A])(f: A => B): AppFunc[F, C, B] =
+  override def map[A, B](fa: AppFunc[F, C, A])(f: A => B): AppFunc[F, C, B] =
     fa.map(f)
   def ap[A, B](f: AppFunc[F, C, A => B])(fa: AppFunc[F, C, A]): AppFunc[F, C, B] =
     Func.appFunc[F, C, B](c => F.ap(f.run(c))(fa.run(c)))(F)
-  def product[A, B](fa: AppFunc[F, C, A], fb: AppFunc[F, C, B]): AppFunc[F, C, (A, B)] =
+  override def product[A, B](fa: AppFunc[F, C, A], fb: AppFunc[F, C, B]): AppFunc[F, C, (A, B)] =
     Func.appFunc[F, C, (A, B)](c => F.product(fa.run(c), fb.run(c)))(F)
   def pure[A](a: A): AppFunc[F, C, A] =
     Func.appFunc[F, C, A](c => F.pure(a))(F)

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

@@ -153,10 +153,10 @@ private[data] sealed abstract class KleisliInstances1 extends KleisliInstances2
     def ap[B, C](f: Kleisli[F, A, B => C])(fa: Kleisli[F, A, B]): Kleisli[F, A, C] =
       fa(f)
 
-    def map[B, C](fb: Kleisli[F, A, B])(f: B => C): Kleisli[F, A, C] =
+    override def map[B, C](fb: Kleisli[F, A, B])(f: B => C): Kleisli[F, A, C] =
       fb.map(f)
 
-    def product[B, C](fb: Kleisli[F, A, B], fc: Kleisli[F, A, C]): Kleisli[F, A, (B, C)] =
+    override def product[B, C](fb: Kleisli[F, A, B], fc: Kleisli[F, A, C]): Kleisli[F, A, (B, C)] =
       Kleisli(a => Applicative[F].product(fb.run(a), fc.run(a)))
   }
 }
@@ -166,7 +166,7 @@ private[data] sealed abstract class KleisliInstances2 extends KleisliInstances3
     def ap[B, C](f: Kleisli[F, A, B => C])(fa: Kleisli[F, A, B]): Kleisli[F, A, C] =
       fa(f)
 
-    def product[B, C](fb: Kleisli[F, A, B], fc: Kleisli[F, A, C]): Kleisli[F, A, (B, C)] =
+    override def product[B, C](fb: Kleisli[F, A, B], fc: Kleisli[F, A, C]): Kleisli[F, A, (B, C)] =
       Kleisli(a => Apply[F].product(fb.run(a), fc.run(a)))
 
     def map[B, C](fa: Kleisli[F, A, B])(f: B => C): Kleisli[F, A, C] =

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

@@ -71,15 +71,15 @@ private[data] sealed abstract class ProdInstances4 {
 sealed trait ProdFunctor[F[_], G[_]] extends Functor[Lambda[X => Prod[F, G, X]]] {
   def F: Functor[F]
   def G: Functor[G]
-  def map[A, B](fa: Prod[F, G, A])(f: A => B): Prod[F, G, B] = Prod(F.map(fa.first)(f), G.map(fa.second)(f))
+  override def map[A, B](fa: Prod[F, G, A])(f: A => B): Prod[F, G, B] = Prod(F.map(fa.first)(f), G.map(fa.second)(f))
 }
 
 sealed trait ProdApply[F[_], G[_]] extends Apply[Lambda[X => Prod[F, G, X]]] with ProdFunctor[F, G] {
   def F: Apply[F]
   def G: Apply[G]
   def ap[A, B](f: Prod[F, G, A => B])(fa: Prod[F, G, A]): Prod[F, G, B] =
     Prod(F.ap(f.first)(fa.first), G.ap(f.second)(fa.second))
-  def product[A, B](fa: Prod[F, G, A], fb: Prod[F, G, B]): Prod[F, G, (A, B)] =
+  override def product[A, B](fa: Prod[F, G, A], fb: Prod[F, G, B]): Prod[F, G, (A, B)] =
     Prod(F.product(fa.first, fb.first), G.product(fa.second, fb.second))
 }
 

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

@@ -254,7 +254,7 @@ private[data] sealed abstract class ValidatedInstances extends ValidatedInstance
       def ap[A,B](f: Validated[E,A=>B])(fa: Validated[E,A]): Validated[E, B] =
         fa.ap(f)(E)
 
-      def product[A, B](fa: Validated[E, A], fb: Validated[E, B]): Validated[E, (A, B)] =
+      override def product[A, B](fa: Validated[E, A], fb: Validated[E, B]): Validated[E, (A, B)] =
         fa.product(fb)(E)
 
       def handleErrorWith[A](fa: Validated[E, A])(f: E => Validated[E, A]): Validated[E, A] =

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

@@ -171,7 +171,7 @@ private[data] sealed trait WriterTApply[F[_], L] extends WriterTFunctor[F, L] wi
 
   def ap[A, B](f: WriterT[F, L, A => B])(fa: WriterT[F, L, A]): WriterT[F, L, B] =
     fa ap f
-  def product[A, B](fa: WriterT[F, L, A], fb: WriterT[F, L, B]): WriterT[F, L, (A, B)] =
+  override def product[A, B](fa: WriterT[F, L, A], fb: WriterT[F, L, B]): WriterT[F, L, (A, B)] =
     WriterT(F0.map(F0.product(fa.run, fb.run)) { case ((l1, a), (l2, b)) => (L0.combine(l1, l2), (a, b)) })
 }
 

core/src/main/scala/cats/free/FreeApplicative.scala

@@ -79,8 +79,8 @@ object FreeApplicative {
 
   implicit final def freeApplicative[S[_]]: Applicative[FA[S, ?]] = {
     new Applicative[FA[S, ?]] {
-      def product[A, B](fa: FA[S, A], fb: FA[S, B]): FA[S, (A, B)] = ap(fa.map((a: A) => (b: B) => (a, b)))(fb)
-      def map[A, B](fa: FA[S, A])(f: A => B): FA[S, B] = fa.map(f)
+      override def product[A, B](fa: FA[S, A], fb: FA[S, B]): FA[S, (A, B)] = ap(fa.map((a: A) => (b: B) => (a, b)))(fb)
+      override def map[A, B](fa: FA[S, A])(f: A => B): FA[S, B] = fa.map(f)
       override def ap[A, B](f: FA[S, A => B])(fa: FA[S, A]): FA[S, B] = fa.ap(f)
       def pure[A](a: A): FA[S, A] = Pure(a)
     }

docs/src/main/tut/apply.md

@@ -26,19 +26,13 @@ implicit val optionApply: Apply[Option] = new Apply[Option] {
     fa.flatMap (a => f.map (ff => ff(a)))
 
   def map[A,B](fa: Option[A])(f: A => B): Option[B] = fa map f
-  
-  def product[A, B](fa: Option[A], fb: Option[B]): Option[(A, B)] =
-    fa.flatMap(a => fb.map(b => (a, b)))
 }
 
 implicit val listApply: Apply[List] = new Apply[List] {
   def ap[A, B](f: List[A => B])(fa: List[A]): List[B] =
     fa.flatMap (a => f.map (ff => ff(a)))
 
   def map[A,B](fa: List[A])(f: A => B): List[B] = fa map f
-  
-  def product[A, B](fa: List[A], fb: List[B]): List[(A, B)] =
-    fa.zip(fb)
 }
 ```
 

docs/src/main/tut/const.md

@@ -219,10 +219,6 @@ implicit def constApplicative[Z]: Applicative[Const[Z, ?]] =
     def pure[A](a: A): Const[Z, A] = ???
 
     def ap[A, B](f: Const[Z, A => B])(fa: Const[Z, A]): Const[Z, B] = ???
-
-    def map[A, B](fa: Const[Z, A])(f: A => B): Const[Z, B] = ???
-
-    def product[A, B](fa: Const[Z, A],fb: Const[Z, B]): Const[Z, (A, B)] = ???
   }
 ```
 
@@ -246,12 +242,6 @@ implicit def constApplicative[Z : Monoid]: Applicative[Const[Z, ?]] =
 
     def ap[A, B](f: Const[Z, A => B])(fa: Const[Z, A]): Const[Z, B] =
       Const(Monoid[Z].combine(fa.getConst, f.getConst))
-      
-    def map[A, B](fa: Const[Z, A])(f: A => B): Const[Z, B] =
-      Const(fa.getConst)
-
-    def product[A, B](fa: Const[Z, A],fb: Const[Z, B]): Const[Z, (A, B)] =
-      Const(Monoid[Z].combine(fa.getConst, fb.getConst))
   }
 ```
 

docs/src/main/tut/validated.md

@@ -199,9 +199,6 @@ implicit def validatedApplicative[E : Semigroup]: Applicative[Validated[E, ?]] =
       }
 
     def pure[A](x: A): Validated[E, A] = Validated.valid(x)
-    def map[A, B](fa: Validated[E, A])(f: A => B): Validated[E, B] = fa.map(f)
-    def product[A, B](fa: Validated[E, A], fb: Validated[E, B]): Validated[E, (A, B)] =
-      ap(fa.map(a => (b: B) => (a, b)))(fb)
   }
 ```
 

laws/src/main/scala/cats/laws/TraverseLaws.scala

@@ -44,11 +44,11 @@ trait TraverseLaws[F[_]] extends FunctorLaws[F] with FoldableLaws[F] {
         val (fm, fn) = f
         (M.ap(fm)(fam), N.ap(fn)(fan))
       }
-      def map[X, Y](fx: MN[X])(f: X => Y): MN[Y] = {
+      override def map[X, Y](fx: MN[X])(f: X => Y): MN[Y] = {
         val (mx, nx) = fx
         (M.map(mx)(f), N.map(nx)(f))
       }
-      def product[X, Y](fx: MN[X], fy: MN[Y]): MN[(X, Y)] = {
+      override def product[X, Y](fx: MN[X], fy: MN[Y]): MN[(X, Y)] = {
         val (mx, nx) = fx
         val (my, ny) = fy
         (M.product(mx, my), N.product(nx, ny))