# @chrilves’ Archives

## Slides

Here are the slides of the talks/workshops i gave:

## Introduction to Types

Why using types? When are they useful? Why we should care about types? What are types? These are the questions [this series of posts]/types/ give some answers to.

# Posts

## Playing with Probability in Scala 3

Here is a simple experiment: take a fair dice (or a coin) and roll it until every side of the dice has been observed at least once. Write down the number of rolls and repeat the operation several times. On average, how many rolls does it take to observe every side of the dice at least once? This is precisely the question we are about to answer together. Solving Maths puzzle is fun.

Soyez les bienvenu·e·s! Cette session a le dessein de vous présenter un outil de programmation très puissant. Alors que la plupart des introductions sur le sujet commencent par une présentation de ses fondements théoriques d’une manière très formelle, nous avons choisi de vous le présenter à travers de courts exemples et des cas d’utilisation concrets. Cet atelier est composé de trois parties. La dernière présente trois des cas d’utilisation des plus utiles.

This workshop will be presented at ScalaIO 2019, in Lyon (France), on Tuesday the 29th of October at 9am. Welcome. This session will introduce you to a very powerful tool in programming. Whereas most introduction start by presenting its theoretical foundations in a very formal way, we chose to present it via short examples and practical use cases. This workshop is made of three parts. The last one presents three of the most valuable use cases.

The Scala source code is at github.com/chrilves/gadt.scala. The Haxe source code is at github.com/chrilves/Gadts.hx. The Web Application is here. Today we will explore the Curry–Howard correspondence. Our mission is writing, in Scala’s type system, the property on natural number of being prime. Wikipedia defines it by: A natural number (1, 2, 3, 4, 5, 6, etc.) is called a prime number (or a prime) if it is greater than 1 and cannot be written as a product of two natural numbers that are both smaller than it.

## Recursion Schemes: the high-school introduction

I gave a talk on Thursday the 28th of march 2019 at the 96th Paris Scala User Group session on about this. The slides are here. Recursion schemes are said to be a tough subject. Articles and presentations often flood the audience with lots of names such as Algebra, CoAlgebra, catamorphisms, anamorhpisms, hylomorphism, etc. Is knowing all these concepts required to understand recursion schemes? I have good news for you: it isn’t!

Generalized Algebraic Data Types (GADT) is certainly one of the most feared concept in programming nowadays. Very few mainstream languages support GADTs. The only ones i know which does are Haskell, Scala, OCaml and Haxe. The idea is actually very simple but often presented in complicated ways. In fact, if you’re familiar to both basic Object-Oriented-with-Generics and basic functional programming, then you most probably are already familiar with GADTs without even knowing you are.

## Let's meet the charming fold family

Today we will meet an amazing family: the fold functions! The well known foldRight Lists is one of the first data structure every developer/computer scientist meet in her/his journey into programming: sealed abstract class List[+A] final case object Nil extends List[Nothing] final case class Cons[+A](head: A, tail: List[A]) extends List[A] It means means values of type List[A] can be of (only) two forms: either Nil or Cons(head, tail) for some values head of type A and tail of type List[A] For example we can define the following lists:

## How to make game in the browser thanks to ScalaJS

A few month ago, the Paris Scala User Group kindly invited me present a workshop introducing [Scala.js(https://www.scala-js.org/). Even better, i had the chance to present it at ScalaIO 2018. The workshop materials are here. I will present how to develop a web application in Scala.js. This talk is for Scala developers having a penchant for web development but rebuffed by JavaScript. It goes from ScalaJS basics to the implementation of a naive virtual DOM written in Scala.

## JSON to XML: the probably a tiny bit over engineered way

The complete code of the article. You need Cats and Play-Json in order to run it. The Slides are here It happens regularly in software development that we have to connect systems speaking different languages. JSON is nowadays ubiquitous in service communication, especially in web development but XML still has its fair amount of bastions. Imagine you need to pass information provided by a JSON API through an XML layer, you need a converter.

## F-Algebra talk at ScalaIO 2017: Modéliser astucieusement vos données

I had the chance to present a talk about F-Algebras at ScalaIO 2017. The Video The Slides