Scala Programming Projects

cats.Applicative

Applicative is a subclass of Apply. It declares an additional function, called pure:

@typeclass trait Applicative[F[_]] extends Apply[F] { 
  def pure[A](x: A): F[A]
}

The pure function puts any value of type A into the F context. A type F that has an instance of Applicative[F] and that respects the associated laws is called an Applicative Functor.

Let's try this new pure function with different F contexts, as follows:

import cats.Applicative
import cats.data.{Validated, ValidatedNel}
import cats.implicits._ 
Applicative[Option].pure(1)
// res0: Option[Int] = Some(1)
3.pure[Option]
// res1: Option[Int] = Some(3)
type Result[A] = ValidatedNel[Throwable, A]
Applicative[Result].pure("hi pure")
// res2: Result[String] = Valid(hi ...