yannick-cw

object DbRepo {
  sealed trait State
  sealed trait Fresh        extends State
  sealed trait IndexCreated extends State
  sealed trait IndexReady   extends State
  sealed trait ReadyToRead  extends State

  def apply(): DbRepo[Fresh] = new DbRepo
}

yannick-cw

import cats.{FlatMap, Monad}
import cats.data.StateT

import scala.concurrent.{Await, Future}
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration.Duration
import cats.implicits._

object ThrottleExp extends App {

yannick-cw

/**
  * Methods vs Functions vs Kleisli  
  */
trait TradingMethods[Account, Market, Order, ClientOrder, Execution, Trade] {
  def clientOrders(order: ClientOrder): List[Order]
  def execute(order: Order, m: Market, a: Account): List[Execution]
  def allocate(execution: Execution, as: List[Account]): List[Trade]

  def tradeGeneration(clientOrder: ClientOrder,
                      market: Market,

yannick-cw

import cats.data.{EitherT, Kleisli}
import common.{Amount, Valid}

import scala.concurrent.ExecutionContext.Implicits.global
import cats.implicits._

import scala.collection.mutable
import scala.concurrent.duration.Duration
import scala.concurrent.{Await, Future}

yannick-cw

import scala.annotation.tailrec

object IOExample extends App {
  import ioInstances._
  case class Player(name: String, score: Int)

  val winner: (Player, Player) => Option[Player] = (p1, p2) =>
    if (p1.score > p2.score) Some(p1)
    else if (p2.score > p1.score) Some(p2)
    else None

yannick-cw

package com.holidaycheck.userflow

import scala.util.Try

object UrlKata {
  case class Protocol(value: String)                extends AnyVal
  case class Domain(value: String)                  extends AnyVal
  case class Params(params: List[(String, String)]) extends AnyVal
  case class Path(value: String)                    extends AnyVal
  case class Url(protocol: Protocol, domain: Domain, params: Params, path: Option[Path] = None)

yannick-cw

import scala.concurrent.{Await, ExecutionContext, Future}
import scala.concurrent.duration.Duration

object FinalTaglessMath extends App {

  trait Math[Container[_]] {
    def value(i: Int): Container[Int]

    def add(a: Container[Int], b: Container[Int]): Container[Int]
  }

yannick-cw

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

yannick-cw

import Ordering.Implicits._

def quicksort[A: Ordering](l: List[A]): List[A] = l match {
  case x :: (xs @ (y :: z)) =>
    val (smallerEq, greater) = xs.partition(_ <= x)
    quicksort(smallerEq) ++ List(x) ++ quicksort(greater)
  case base => base
}

yannick-cw

select rental_id, return_date
from rental
where return_date is null;

select title, rating
from film
where ( rating != 'G' and rating != 'PG' ) or rating is null;

select first_name , last_name 
from customer