wennergr

G   H   I   J
 \ /     \ /
  D   E   F
   \  |  / \
    \ | /   |
     \|/    |
      B     C
       \   /
        \ /
         A

wennergr

import cats.std.all._
import cats.syntax.option._
import cats.syntax.apply._
import cats.data.Validated._

val a = 1
val b = 2

// Intellij(15) are happy, no red red squiggly.
val ab = (a.some |@| b.some) map { _ + _ }

wennergr

Keybase proof

I hereby claim:

• I am wennergr on github.
• I am wennergr (https://keybase.io/wennergr) on keybase.
• I have a public key whose fingerprint is 585F 4750 72B2 5C2F 0463 71CC 88CE 2E10 D296 5051

To claim this, I am signing this object:

wennergr

case class Name(firstName: String, lastName: String)
case class Address(street: String, zip: String, state: String)

case class User(name: Name, address: Address)

def getName(id: Long): IO[Name] = /* ... */
def getAddress(id: Long): IO[Address] = /* ... */

val user: IO[User] = ???

wennergr

for {
  x <- List(1,2,3)
  y <- List(4+x,5+x,6+x)
} yield(y) // List(5, 6, 7, 6, 7, 8, 7, 8, 9)

for {
  firstName <- Some("Bob")
  lastName <- Some("Axel")
} yield firstname + " " + lastName // Some("Bob Axel")

wennergr

// Dependent programs. I need to know `x` to calculate `y`
for {
  x <- List(1,2,3)
  y <- List(4+x,5+x,6+x)
} yield(y) // List(5, 6, 7, 6, 7, 8, 7, 8, 9)

// Independent programs. No need to know `firstName` to get `lastName`
for {
  firstName <- Some("Bob")
  lastName <- Some("Axel")

wennergr

trait Applicative[F[_]] extends Functor[F] {
  def pure[A](x: A): F[A]
  def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]
}

wennergr

trait Applicative[F[_]] extends Functor[F] {
  def pure[A](x: A): F[A]
  def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]  
  def map2[A, B, Z](fa: F[A], fb: F[B])(f: (A, B) => Z): F[Z] =
      ap(map(fa)(a => (b: B) => f(a,b)))(fb)
}

wennergr

// Monad version
for {
  firstName <- Some("Bob")
  lastName <- Some("Axel")
} yield firstname + " " + lastName // Some("Bob Axel")

// Applicative functor version
Applicative[Option].map2(Some("Bob"), Some("Axel"))((a,b) => a + " " + b) // Some("Bob Axel")

wennergr

import cats._, cats.implicits._, cats.effect.IO

case class Name(firstName: String, lastName: String)
case class Address(street: String, zip: String, state: String)
case class User(name: Name, address: Address)

def getName(id: Long): IO[Name] = /* Call third party API */
def getAddress(id: Long): IO[Address] = /* Call third party API */

val userId = 100L