haskell-training

Material for a Haskell training course

Haskell at work

The course proposes a practical approach to Haskell, a statically typed purely functional programming language. The course develops around the creation and evolution of a concrete project, highlighting where Haskell can help us to create a safe and maintainable application. It will contain the necessary theory and a lot of practice.

The course will introduce some more advanced concepts (e.g. type-level programming with Servant) but it would focus mostly on the day-to-day aspects of the language, which allow a programmer to become productive sooner.

Everything will be developed with the good practices of software engineering in mind.

Principles

• create a practical application which resembles what people could do at work;
• try not to over-abstract before it is needed;
• introduce concepts only when they solve an issue (see https://mkremins.github.io/blog/doors-headaches-intellectual-need/);
• introduce concepts one by one;

Objectives

• give the participants the feeling of how it is to work with Haskell
• teach them the basics of Haskell development and how to solve practical problems
• teach correct and precise data modelling using types
• show them the best features of Haskell
• provide directions on how to develop a real-world project
• discuss shortcomings/limitations of the language

Target

• professional developers
• already experienced with some other programming language
• possibly willing to use Haskell or FP concepts at work
• interested in why Haskell is a good language for the industry
• interested also in the practicalities

Buyers

• single developers who want to get a practical approach to Haskell
• companies interested in starting using Haskell
• companies using Haskell wanting to train their junior developers

Prerequisites

• a bit of software engineering experience
  • knowledge of what is required for a production system
• already felt the pains of mutation and side effects management
• some experience in other languages with basic FP concepts such as immutability and higher-order functions
• basic Haskell syntax

Project

The course will unroll developing a simplified clone of a questionnaire app like Google Forms or Typeform.

It adapts well to the principles we stated above since:

• it is extremely practical and concrete
• allows to be modelled in simple way which still highlights the usage of algebraic data types
• requires user interaction
• requires persistence
• requires definition of a web API

Outline

• Chapter 1: Basic domain definition and terminal interaction
  • Haskell syntax and basic terminology
  • the value of types and purity
  • IO and side-effects
  • Chapter 2: Domain refinement and exposing a web API with Servant
    • defining a domain model guided by types
    • defining a web API specification using types
    • how to isolate the domain layer from persistence
    • functors and applicatives
  • Chapter 3: Adding persistence with PostgreSQL
    • describing a database schema in Haskell
    • writing composable queries
    • monads and monad transformers
  • Chapter 4: Testing and tooling
    • the easiness of writing unit tests
    • property based testing
    • doctests
    • mocks
  • Bonus chapter: Advanced type safety (to solve a concrete modelling problem)
    • GADTs
    • RankNTypes
    • Existential types

Length

The basic version of the course, without the bonus chapters, should take around two days, split in four chapters of ~ 4 hours each.

It could be enlarged to 3 days (6 chapters of ~ 4 hours each) adding the two bonus chapters