BalmungSan

Why Functional Programming?

Probably not the most poetic nor academic or well written phrase, but let me express in plain English why I end up choosing Functional Programming.

Over my time coding (which I have to clarify that has been short) I have learned two important things about code.
(mostly from the experience of many more veteran colleagues)

1. The best line of code is the one that is not written. Why? Because, every single line of code that you write is instant technical debt. No matter, how well done it is, how well designed it was, how much of 1000x programmer you are, all the code is debt. All the code will become obsolete at some point in time, all the code has to be refactored.

BalmungSan

// IO: A Monad for side-effects.
import $ivy.`org.typelevel::cats-effect:1.3.1`

import cats.effect.IO
import scala.concurrent.ExecutionContext

implicit val IOTimer = IO.timer(ExecutionContext.global)
implicit val IOShift = IO.contextShift(ExecutionContext.global)
// ----------------------------------------------

BalmungSan

Polymorphism in Scala

This document aims to show and compare three alternatives for achieving polymorphism in Scala.

• Subtyping, common in object-oriented languages like Java.
• Duck typing, common in dynamically typed languages like Python.
• Typeclasses, common in functional languages like Haskell.

Additionally, when implementing the typeclass pattern in Scala,

BalmungSan

//> using scala "2.13.10"
//> using lib "org.typelevel::cats-effect:3.3.14"
//> using lib "co.fs2::fs2-core:3.4.0"
//> using lib "org.neo4j.driver:neo4j-java-driver:5.3.0"

import cats.effect.IO
import fs2.Stream
import org.neo4j.driver.summary.ResultSummary
import org.neo4j.driver.types.{IsoDuration => NeoDuration, Point => NeoPoint}

BalmungSan

What is a Monad and why you shouldn't care

People trying to learn about FP will heard about the M word sooner than latter. Personally I believe that way sooner than what is required, and recommended; which is what makes folks to be confused about it.

This is my humble attempt to try to briefly explain the concept, while also arguing that you shouldn't really care too much about it. This all with the intention to make your FP journey more enjoyable 😄 — without further ado, let's start.

Motivation behind Monads

BalmungSan

import cats.effect.IO
import io.circe.Encoder
import io.circe.generic.semiauto.deriveEncoder
import io.circe.java8.time.encodeZonedDateTimeDefault
import io.circe.syntax.EncoderOps
import org.bson.{BsonReader, BsonType, BsonWriter}
import org.bson.codecs.{DecoderContext, Codec, EncoderContext}
import org.bson.codecs.configuration.{CodecConfigurationException, CodecRegistries}
import org.mongodb.scala.MongoClient
import org.mongodb.scala.bson.codecs.{DEFAULT_CODEC_REGISTRY, Macros}

BalmungSan

// scala 2.13.6

sealed trait RockPaperScissorsMove extends Product with Serializable
object RockPaperScissorsMove {
  final case object Rock extends RockPaperScissorsMove
  final case object Paper extends RockPaperScissorsMove
  final case object Scissors extends RockPaperScissorsMove
}

trait Game {

BalmungSan

package example

import cats.effect.IO
import cats.effect.kernel.Ref
import cats.syntax.all._

import scala.concurrent.duration._

object MultiTaskRunner {
  /** Allows a task to report its progress. */

BalmungSan

import cats.Applicative
import cats.effect.IO
import fs2.Stream
import io.circe.Encoder
import io.circe.generic.semiauto.deriveEncoder
import io.circe.syntax.EncoderOps
import org.http4s.{EntityEncoder, MediaType}
import org.http4s.dsl.io._
import org.http4s.headers.`Content-Type`

BalmungSan

package example

import cats.effect.Async
import cats.effect.std.Queue
import cats.effect.syntax.all._
import cats.syntax.all._

import scala.concurrent.ExecutionContext

object HighLowPriorityRunner {