Unwrapping Monads & Friends
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Unwrapping Monads & Friends

Shining Light on Functional Programming's Scariest Concepts

About the Book

Unwrapping Monads & Friends is a deep-yet-friendly guide to one of functional programming’s most notoriously misunderstood topics: the monad. Written with clarity, empathy, and a healthy dose of pragmatism, this book breaks through the fog of intimidating jargon and dense formalism to offer a clear, grounded understanding of what monads actually are—how they work, why they matter, and how they can improve the way we write and think about code.

This isn’t just "yet another monad tutorial." It’s a practical journey through the conceptual landscape of monads and their closely related "friends"—including functors, foldables, and applicatives—anchored in real JavaScript examples and a gradual learning curve. Whether you’ve struggled through Haskell-heavy blog posts or are just FP-curious, this guide offers a fresh path forward, revealing the power and elegance of these patterns without requiring a math degree or prior exposure to category theory.

Brought to you by Kyle Simpson, author of Functional-Light JavaScript and the You Don’t Know JS series (2 editions), this guide distills years of learning, teaching, and practical application into a concise and illuminating read. It’s ideal for anyone who’s FP-aware and ready to go deeper—especially those who’ve bounced off monads before and are ready to finally see what all the fuss is about.

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    • Functional Programming
    • JavaScript
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About the Author

Kyle Simpson
Kyle Simpson

Kyle Simpson is a web-oriented software engineer, widely acclaimed for his "You Don't Know JS" book series and nearly 1M hours viewed of his online courses. Kyle's superpower is asking better questions, and he deeply believes in maximally using the minimally-necessary tools for any task. As a "human-centric technologist", he's passionate about bringing humans and technology together, evolving engineering organizations towards solving the right problems, in simpler ways. Kyle will always fight for the people behind the pixels.

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Table of Contents

  • Intro
  • Chapter 1: FP primer
    • From Loop To Map And Filter
    • Where To Learn More FP?
    • How Do I Know…?
  • Chapter 2: What is a monad?
    • What Is Monad?
    • Simplest JS Illustration
    • Building Up Monads
    • Monadic Chain
    • Back To The Core Of Monad
  • Chapter 3: Monads illustrated
    • Maybe Something More?
    • Reader Monad
    • Statefully Monadic
  • Chapter 4: I know IO (monad)!
    • I/O with IO
    • Non-Value-Container?
    • But Why IO?
    • Monad Summary
  • Chapter 5: Friends of monads
    • Foldable
    • Concatable (Semigroup)
    • Applicative
  • Wrapping up!

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