Jules Ivanic guizmaii

Shared State in pure Functional Programming

Newcomers to Functional Programming are often very confused about the proper way to share state without breaking purity and end up having a mix of pure and impure code that defeats the purpose of having pure FP code in the first place.

Reason why I decided to write up a beginner friendly guide :)

Use Case

We have a program that runs three computations at the same time and updates the internal state to keep track of the

Applied Functional Programming with Scala - Notes

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

	import com.lightbend.lagom.scaladsl.persistence.{PersistentEntity, PersistentEntityRef}
	import monix.eval.Task
	import play.api.libs.json.Format

	object SingletonEntityRegistry {

	implicit final class SingletonEntityRegistry(val registry: PersistentEntityRegistry) extends AnyVal {
	def singletonRefFor[T <: SingletonEntity: ClassTag]: PersistentEntityRef[T#Command] =
	registry.refFor[T](SingletonEntity.id.underlying)
	}

	package net.degoes

	import scalaz.Scalaz._
	import scalaz._
	import scalaz.zio._

	import scala.io.{Codec, Source}
	import scala.language.higherKinds
	import scala.util.{Failure, Success, Try}

	package net.degoes

	import scalaz.zio._

	import scala.io.{Codec, Source}
	import scala.util.{Failure, Success, Try}
	import scalaz._
	import Scalaz._

	/**

	Puma::Plugin.create do
	def production?
	ENV.fetch('RACK_ENV', 'development') == 'production'
	end

	def log(msg)
	if production?
	Rails.logger.info msg
	else
	puts msg

	Flat profile of 398.33 secs (23810 total ticks): Ruby-0-JIT-1

	Interpreted + native Method
	0.7% 8 + 0 org.jruby.ir.targets.IRBytecodeAdapter6.pushBoolean
	0.4% 5 + 0 java.lang.Class.getDeclaredFields0
	0.3% 4 + 0 org.jruby.ir.targets.JVMVisitor.PushMethodBindingInstr
	0.3% 3 + 0 org.jruby.ir.targets.JVMVisitor.oneFixnumArgNoBlockCallInstr
	0.3% 3 + 0 org.jruby.ir.representations.CFG.build
	0.3% 3 + 0 java.util.regex.Pattern.split
	0.2% 2 + 0 org.jruby.ir.targets.JVMVisitor.RescueEQQInstr

	=> Booting Puma
	=> Rails 4.2.10 application starting in production on http://localhost:3000
	=> Run `rails server -h` for more startup options
	=> Ctrl-C to shutdown server
	E, [2018-11-27T17:20:38.796620 #93071] ERROR -- ddtrace: [ddtrace] (/Users/jules/.rvm/gems/jruby-9.1.17.0/gems/ddtrace-0.17.2/lib/ddtrace/transport.rb:212:in `log_error_once') Connection refused - Failed to open TCP connection to 127.0.0.1:8126 (Connection refused - connect(2) for "127.0.0.1" port 8126)
	Puma starting in single mode...
	* Version 3.12.0 (jruby 9.1.17.0 - ruby 2.3.3), codename: Llamas in Pajamas
	* Min threads: 16, max threads: 16
	* Environment: production
	* Listening on tcp://localhost:3000

	#!/usr/bin/env ruby -w
	require "benchmark"

	TIMES = 100_000
	ARRAY = (1..1_000).to_a

	Benchmark.bm(30) do \|b\|
	b.report "each" do
	TIMES.times do \|i\|
	ARRAY.each do \|element\|