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Replace Nested code with ??? stubs #16

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Replace Nested code with ??? stubs #16

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12 changes: 3 additions & 9 deletions src/main/scala/learnfp/nested/Nested.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -13,21 +13,15 @@ case class Nested[F[_], G[_], A](value:F[G[A]])
object Nested {
implicit def functorInstance[F[_], G[_], A](implicit fF: Functor[F], fG: Functor[G]) =
new Functor[({type E[X] = Nested[F, G, X]})#E] {
override def fmap[A, B](a: Nested[F, G, A])(fx: A => B): Nested[F, G, B] = Nested[F, G, B] {
fF.fmap(a.value) { xg => fG.fmap(xg) { x => fx(x) } }
}
override def fmap[A, B](a: Nested[F, G, A])(fx: A => B): Nested[F, G, B] = ???
}

implicit def applicativeInstance[F[_], G[_], A](implicit fA:Applicative[F], gA:Applicative[G],
fF:Functor[F], gF:Functor[G],
) =
new Applicative[({type E[X] = Nested[F, G, X]})#E] {
override def pure[A](a: A): Nested[F, G, A] = Nested(fA.pure(gA.pure(a)))
override def <*>[A, R](nfx: Nested[F, G, A => R])(na: Nested[F, G, A]): Nested[F, G, R] = {
lazy val fxfg:F[G[A=>R]] = nfx.value
lazy val afg:F[G[A]] = na.value
Nested({ (fx:G[A=>R], a:G[A]) => fx <*> a }.curried `<$>` fxfg `<*>` afg)
}
override def pure[A](a: A): Nested[F, G, A] = ???
override def <*>[A, R](nfx: Nested[F, G, A => R])(na: Nested[F, G, A]): Nested[F, G, R] = ???
}

/* We can not nest monads, we should use monad transformers to achieve nesting */
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