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Functional Programming Fundamentals in Kotlin with Arrow


Functional Programming Fundamentals in Kotlin with Arrow

In this intensive course, we’ll cover Functional Programming essentials in Kotlin over four days / 16-hrs total. By the end of this course, you will have a solid grasp on the course concepts.

Course Dates:

  • Tuesday, July 27th - 09:00 - 13:00 CET
  • Wednesday, July 28th - 09:00 - 13:00 CET
  • Thursday, July 29th - 09:00 - 13:00 CET
  • Friday, July 30th - 09:00 - 13:00 CET

Course content

Lesson 1: Functional Programming

Functional programming fundamentals.​

  • What is it, what is it good for.
  • Pure functions.
  • Side effects.
  • Referential transparency & substitution model.
  • Local reasoning.
  • Is Kotlin a functional language?
  • Higher order functions.
  • Deferring execution.
  • Exercises.
Lesson 2: Domain Modeling

Modeling our domain from a functional perspective.

  • Kotlin type system. Leveraging compiler aid via types.
  • Modeling concerns and making them explicit with types.
  • Unit and Nothing to model meaningful scenarios.
  • Inline classes for type safety and preciseness.
  • Algebraic Data Types: Product and Sum types.
  • Complexity of ADTs.
  • Modeling choice and control flow with sum types.
  • Arrow data types as ADTs.
  • Eliminating bugs and tests for invariants via type safety.
  • Exercises.
Lesson 3: Immutable Data and Optics

Optimizing reusability and composition for immutable data structures using Optics.

  • Immutability.
  • Issues with Kotlin data class copy.
  • Optics for working efficiently with nested immutable data.
  • Optics composition and reusability.
  • The Optics DSL.
  • Stacking optics to create more powerful ones 🔭
  • Lens for reading / modifying nested data.
  • Prism for conditional reading / modification.
  • Optional as the composition of Lens and Prism.
  • Every for working over lists of elements.
  • FilterIndex for working over lists of elements based on a predicate.
  • Index for reading or modifying elements obtained by their index.
  • Iso for isomorphic conversions.
  • Exercises.
Lesson 4: Domain Modeling II - Error Handling

Learning how to model and handle errors in functional programs.

  • Railway oriented programming 🚂 - Happy path vs alternative path.
  • Making errors vs success explicit with types.
  • The Either datatype.
  • Exhaustive evaluation.
  • Either composition and computational blocks (bindings).
  • Either bias towards the happy case.
  • Capturing third party library errors.
  • Mapping third party errors to strongly typed domain errors.
  • Error accumulation.
  • Validated and ValidatedNel.
  • Either and Validated, when to use each? Fail fast vs error accumulation.
  • Either and Validated interoperability.
  • Flattening lists of Either or Validated.
  • Either or Validated for domain model validation.
  • Modeling potential absence of a value.
  • Exercises.
Lesson 5: Functional Effects

Keeping side effects under control.

  • Recap on side effects.
  • Suspend for tracking effects at compile time.
  • The benefits of modeling effects with suspend.
  • Making effect declaration pure.
  • Concern separation - pure logics vs runtime.
  • Internals of suspend - Continuation passing style.
  • The impact of suspend in architecture.
  • Leveraging Either and Validated in suspended contexts.
  • Arrow integration with KotlinX Coroutines.
  • Structured concurrency & cancellation via KotlinX Coroutines.
  • Providing a runtime for our suspended program.
  • Functional effect operators via Arrow Fx.
  • Parallel computations, races, repeating and retrying suspended effects.
  • Handling errors in suspended contexts.
  • Exercises.
Lesson 6: Safe Resource Handling

Functional operators to work safely with resources across boundaries.

  • What is a resource?
  • The issues of working with resources in concurrent contexts.
  • Why try / catch is not enough.
  • Acquiring, using, and releasing a resource.
  • Abstraction as a means to leverage composability.
  • Ensuring resource disposal to avoid leaks.
  • bracket and bracketCase operators.
  • guarantee and guaranteeCase operators.
  • Limitations of bracket and bracketCase.
  • Resource data type.
  • Resource and bracket to work with third party libraries.
  • Exercises.
Lesson 7: Functional Streams

Streams able to embed and evaluate functional effects.

  • The need for streams.
  • The need for suspend support in streams.
  • Streams in Kotlin via Flow data type.
  • Modeling functional effects within a Flow.
  • Flows are cold.
  • Consuming functional streams safely - suspend terminal operators.
  • Flow integration with Arrow Fx operators.
  • Cancellation of streams with functional effects via structured concurrency.
  • Sneak peek into Flow builders and operators.
  • Composing Flows together.
  • Error path vs happy path in the context of a Flow.
  • Retrying Flows.
  • Exercises.
Lesson 8: Functional Architecture

How to organize and structure functional programs.

  • Concern separation from an architecture perspective.
  • Keeping architecture pure edge to edge.
  • The concept of algebras.
  • Isolating side effects, pushing them to the edges.
  • Dependency injection in functional codebases.
  • Replacing side effects with test doubles.
  • The importance of pure functions and determinism for testing.
  • The importance of a precise self validated domain for testing.
  • Removing tests for invariants with proper types.
  • Testing functional codebases.
  • Sneak peek into Property Based Testing (PBT) with Kotest.
  • Generating input data for our tests.
  • Failure shrinking to track down failing cases.
  • Detecting edge cases thanks to PBT.
  • Exercises.

  • $1100
  • -50%

Enroll for $550Starts on July 27 at 09:00 - 13:00 CET

Company and Private Group Training


Jorge Castillo

Jorge Castillo

Senior Software Engineer


  • Kotlin
  • Functional Programming Essentials
  • Type classes
  • Error Handling
  • Output

This Instructor-Led Course includes:

  • Maximum Class Size of 15
  • Access to Academy EduTools Platform
  • Access to Course Materials
  • Certificate of Completion
  • Access to the Academy Slack


  • One year of experience using Kotlin or similar Functional Programming-oriented languages
  • coroutines
  • structured concurrency
  • coroutine scopes
  • dispatchers
  • cancellation
  • suspend
  • Flow

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