Course Overview

With this course we will be covering a range of topics that will give you a solid grounding in Scala Cats and Cats-Effect 3. Not only will you receive an introduction to Category Theory, Cats, Cats Effects, but we will also go through Tagless Final Encoding to give you a well-rounded overview. This course has been designed to give you as comprehensive an introduction as possible while still leaving time and space for questions and discussion.

Course Prerequisites

Students should be familiar with the Scala programming language (preferable version 3). You should in particular be familiar with aspects such as type-classes and context bounds. It is a great course for student preparing to use Scala libraries such as fs2, http4s, ZIO, AKKA/Pekko etc

Outline

Scala Recap (if needed)

Type constructors
Higher-kinded types
Type classes in Scala
Context bounds

Introduction to Cats

Understand the scope and intent of Cats
Explain the structure of the library
List cats modules
Various import approaches
List and discuss related projects
Using a Cats Type class
Defining your own instance
Discuss ID Operations
List various small enhancements to Scala (e.g, for Either/Option)
Introduce Monoids and Semigroups

Cats Functors, Applicatives, Traverse and Monads

Functors

Introduce Functors in terms of Categories
Use Endofunctor in Programming
Introduce the functor laws
Introduce the Cats Functor Type class
Using derived methods (lift, as, …)
Introduce Natural Transformations
Understand FunctionK
Combing Functors using the Nested type
Introduce Bifunctors
Using bifunctors with ADTs

Applicatives and Traverse

Introduce the Applicative functor
compose independent effects
Using product/tuple functions
Using mapN functions
Replicating Applicatives
Composing Applicatives
Introduce Traverse
Using Traverse sequence

Monads

Recap Kleisli
Introduce Monads
Introduce the monad laws
composing dependent effects using Monads
Writing tail-recursive Monads

Cats Core Data Types

Validated

Using Validated to accumulate errors
Understand the role of sequence
Using the Chain and NonEmptyChain

Parallel

Understand the need to Parallel
Recap FunctionK and Natural Transformations
Using parallel operations on Monads (e.g, parProduct, parSequence etc)

Eval

Using Eval to control synchronous evaluation
Understand the concept of trampolining
Understand the concepts of now, later, always
Using defer to lift a value into 'Eval'

Monad Transformers

Understand the role of Monad Transformers
Composing Monads using Transformers
Use transformers to stack effects
List bundled transformers (OptionT, EitherT, ..)
Caveats and alternatives

Reader, Writer and State Monads

Turning functions into monads using Reader
Use the Reader for implicit contextual objects (e.g., configuration)
Using the Reader for dependency injection (with effect tracking)
Using ReaderT to stack other effects
Understand the relation between Reader, Kleisli nad the identity monad
Introduce the Writer monad
Using the writer for audit trails

Raising and Handling Errors

Introduce the ApplicativeError and MonadError
Raising errors
Handling errors
Transforming errors (e.g, to Either)
Using an error-tap

Dealing with Side Effects (Cats Effect)

What are effects?
Challenges with effects and Functional Programming
Side effects and Referential Transparency
Introduce Cats Effect
Understand the relation with Cats

Introduce the IO Monad

Introduce the IO Monad reference implementation
Trampolining and IO
Understand the different execution styles (pure, lazy, async)
Introduce Fibers
Understand non-preemptive multitasking
Understand the problems with JVM Threads and Concurrency
Introduce green-threads and fibers
Discuss best practices for application thread-pools
Introduce the IOApp and IOApp.Simple

The Effect Type Classes

Provide an overview of the Cats effect type classes (MonadCancel, Spawn, Concurrent, Sync, Async etc.)
List and introduce the other type classes (e.g., Unique[F], Clock[F], …)
Using Console[F] from the Cats effect standard library
Writing polymorphic code using context bounds
Discuss logging (log4cats)

Cancellation (MonadCancel[F])

Recap MonadError
Understand the concept of fiber cancellation
Apply masking using uncancelable
Appreciate the concept of *polling
Introduce the Bracket use case
Understand nested brackets

Resource (Data type)

Introduce and use the Resource type
Building Resources
Composing Resources

Sync[F]

Recap the type-classes on which Sync[F] is based
Suspending effects
Suspending blocking effects
Building cancable blocking effects
Understand context shifting

Suspending fibers (Temporal[F])

Understand the concept of semantic blocking
Using combinators such as sleep, delayBy etc.
Using alternative effects in time-outs

Fibers (Spawn[F])

Recap Fibers
Creating fiber using Spawn[F]
Understand the Spawn[F] algebra
Joining multiple fibers
Cancelling fibers
Understand the Fiber OutCome
Race multiple fibers
Appreciate the Parallel implementation for Spawn[F]
Recap Parallel[F]
Using Parallel[F] with Spawn[F] (parMap, parTraverse, etc.)

Concurrent State (Concurrent[F])

Introduce the Concurrent[F] type-class
Using Ref to share mutable state between fibers
Understand Ref and the benefits over traditional locking
Appreciate atomic updates to the Ref
Using Deferred communicate between fibers
Understand the difference between Ref and Deferred
Discuss various scenarios for using the constructs
Memoization effects using Concurrent[F]
Using bounded versions of Parallel operations (e.g., parReplicateAN, parTraverseN etc.)

Asynchronous effects (Async[F])

Introduce the Async[F] type-class
using callbacks for asynchronous code
Add cancellation and finalization to asynchronous code
Integrate with legacy Futures and CancelableFuture
Understand context shifting
Shifting between thread pools

Tagless Final

Understand the theory behind TF
Discuss Initial vs Final encoding
Appreciate Tagged vs Tagless
Encode your algebra using TF
Discuss laws
Using TF with Cats/ Cats Effect
Discuss various Encoding styles (functions, modules, traits etc)

Scala Cats and Cats-Effect 3.x

2 days