CODEWITHSUNDEEP
scalafunctional-programmingscalazapplicative
Adrian
Adrian

Reputation: 5681

What methods are needed to create custom Applicative Functor to use with scalaz |@|

I would like to be able to do use scalaz's |@| on my own applicative functor.

Example:
val spread: Source[Yield] = (y2 |@| y1)(_ - _)

This is my class 

sealed abstract class Source[+A] {
  def map[B](f: A => B): Source[B] 
  def unit[A](a: A): Source[A]
  def pureList[A](la: List[A]): Source[A]
  def zero[A]: Source[A]
  def map2[A, B, C](as: Source[A], bs: Source[B], f: (A, B) => C): Source[C]
}

I'm certain I have to implement map because it's a functor.
An applicative can be implemented in various ways: for example using apply() and unit() or map2() and unit().

Do I need ap and pure as well?

As you can see I'm not sure what is needed.

Upvotes: 4

Views: 137

Answers (1)

OlivierBlanvillain
OlivierBlanvillain

Reputation: 7768

implicit val mya = new Applicative[Source] {}

Let the compiler answer that question for you:

object creation impossible, since:
it has 2 unimplemented members.
/** As seen from <$anon: scalaz.Applicative[Source]>, the missing signatures are as follows.
 *  For convenience, these are usable as stub implementations.
 */
  // Members declared in scalaz.Applicative
  def point[A](a: => A): Source[A] = ???

  // Members declared in scalaz.Apply
  def ap[A, B](fa: => Source[A])(f: => Source[A => B]): Source[B] = ???

Upvotes: 6

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