arosien

import cats.effect.IO
import java.io.ByteArrayOutputStream

val out = new ByteArrayOutputStream
val cookies = IO(println("cookies"))
Console.withOut(out) { cookies.unsafeRunSync() }
out.toString // "cookies\n"

arosien

Functional Programming Demystification

• Scala at the Sea: 19 May 2020
• Adam Rosien @arosien
• Inner Product @InnerProductLLC inner-product.com

Functional programming is full of Fancy Words™. Let's collect a list of them to demystify together. Adam will facilitate with live-coding, and will also try to make good jokes.

Here's some terms to bootstrap us: effect, free monad, functor, property-based testing, refinement type, stream, etc. >

arosien

case class RoseF[V, A](root: V, children: List[A])

object RoseF {
  type Fixed[V] = Fix[RoseF[V, ?]]

  implicit def traverse[V]: Traverse[RoseF[V, ?]] =
    new DefaultTraverse[RoseF[V, ?]] {
      def traverse[G[_]: Applicative, A, B](
          fa: RoseF[V, A]
      )(f: A => G[B]): G[RoseF[V, B]] =

arosien

@startuml
concise "Client" as Client
concise "Server" as Server
concise "Response freshness" as Cache

Server is idle
Client is idle

@Client
0 is send

arosien

import cats._
import cats.implicits._

/*
            Box a: forall b. (a -> b)   -> b
    Codensity f a: forall b. (a -> f b) -> f b
       Yoneda f a: forall b. (a -> b)   -> f b

    https://stackoverflow.com/questions/45287954/is-having-a-a-b-b-equivalent-to-having-an-a
 */

arosien

import cats._
import cats.data._
import cats.implicits._

object KleisliReader {
  val k = Kleisli[Id, Int, String](i => (i + 1).toString)
  
  Contravariant[Reader[?, String]]      // not found
  Contravariant[Kleisli[Id, ?, String]] // not found

arosien

Scala at the Sea: 8 Jan 2019

Adam Rosien @arosien Inner Product LLC

Can you read this? How about you over there? :thumbs_up:

Type-level programming

What is type-level programming?

arosien

import $ivy.`org.typelevel::cats-core:1.4.0`
import cats._
import cats.data._
import cats.implicits._

// compose "regular" functions:

def a(s: String): Int = s.length
def b(i: Int): Int = i + 1
def c(i: Int): String = i.toString + "!"

arosien

Variance: OOP vs. FP

TODO: introduction

Note: the examples below use the following algebraic data type:

sealed trait Shape
case class Circle(radius: Double) extends Shape
case class Rectangle(height: Double, width: Double) extends Shape

arosien

/*
 * Algebraic Data Types
 */

// A has a B and C
case class A(b: B, c: C)

// A is a B or C
sealed trait A
case class B() extends A