Practical FP in Scala: A hands-on approach
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Practical FP in Scala: A hands-on approach

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About the Book

Practical FP in Scala: A hands-on approach, is a book for intermediate to advanced Scala developers. Aimed at those who understand functional effects, referential transparency and the benefits of functional programming to some extent but who are missing some pieces to put all these concepts together to build a large application in a time-constrained manner.

Throughout the chapters we will design, architect and develop a complete stateful application serving an API via HTTP, accessing a database and dealing with cached data, using the best practices and best functional libraries available in the Cats ecosystem.

You will also learn about common design patterns such as managing state, error handling and anti-patterns, all accompanied by clear examples. Furthermore, at the end of the book, we will dive into some advanced concepts such as MTL, Classy Optics and Typeclass derivation.

The book is supplemented by two Scala projects:

Got some feedback? Please email the author here: pfpscala at gmail dot com.

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About the Author

Gabriel Volpe
Gabriel Volpe

Gabriel Volpe is a Software Engineer, specialized in functional programming, from Buenos Aires, Argentina. He has been writing code since 2005, using Scala professionally since 2014 and Haskell since 2017. He is also the author of some open-source Scala libraries such as Fs2 Rabbit and Redis4Cats. You can find him giving talks at functional programming conferences and meetups all over the world as well as helping people out on Gitter.

Table of Contents

  • Preface
  • Acknowledgments
  • Dependency version
  • Prerequisites
  • How to read this book
    • Conventions used in this book
  • 1. Chapter 1: Shopping Cart project
    • 1.1 Business requirements
      • 1.1.1 Third-party Payments API
      • 1.1.2 Identifying the domain
      • 1.1.3 Identifying Http endpoints
    • 1.2 Architecture
    • 1.3 Technical stack
      • 1.3.1 A note on Cats Effect
  • 2. Chapter 2: Design patterns
    • 2.1 Strongly-typed functions
      • 2.1.1 Value classes
      • 2.1.2 Newtypes
      • 2.1.3 Refinement types
    • 2.2 Encapsulating state
      • 2.2.1 In-memory counter
    • 2.3 Sequential vs concurrent state
      • 2.3.1 State Monad
      • 2.3.2 Atomic Ref
    • 2.4 Shared state
      • 2.4.1 Regions of sharing
      • 2.4.2 Leaky state
    • 2.5 Anti-patterns
      • 2.5.1 Seq: a base trait for sequences
      • 2.5.2 About Monad Transformers
    • 2.6 Error handling
      • 2.6.1 MonadError and ApplicativeError
      • 2.6.2 Either Monad
      • 2.6.3 Classy prisms
  • 3. Chapter 3: Tagless final encoding
    • 3.1 Algebras
      • 3.1.1 Naming conventions
    • 3.2 Interpreters
      • 3.2.1 Building interpreters
    • 3.3 Programs
    • 3.4 Implicit vs explicit parameters
      • 3.4.1 Achieving modularity
      • 3.4.2 Implicit convenience
  • 4. Chapter 4: Business logic
    • 4.1 Identifying algebras
    • 4.2 Data access and storage
    • 4.3 Defining programs
      • 4.3.1 Checkout
      • 4.3.2 Retrying effects
  • 5. Chapter 5: HTTP layer
    • 5.1 A server is a function
    • 5.2 HTTP Routes #1
    • 5.3 Authentication
      • 5.3.1 JWT Auth
    • 5.4 HTTP Routes #2
    • 5.5 Composing routes
    • 5.6 Middlewares
      • 5.6.1 Compositionality
    • 5.7 Running server
    • 5.8 Entity codecs
      • 5.8.1 JSON codecs
      • 5.8.2 Validation
    • 5.9 HTTP Client
      • 5.9.1 Payment client
      • 5.9.2 Creating a client
  • 6. Chapter 6: Persistent layer
    • 6.1 Skunk & Doobie
      • 6.1.1 Session Pool
      • 6.1.2 Queries
      • 6.1.3 Commands
      • 6.1.4 Interpreters
      • 6.1.5 Streaming & Pagination
    • 6.2 Redis for Cats
      • 6.2.1 Connection
      • 6.2.2 Interpreters
    • 6.3 Blocking operations
    • 6.4 Health check
  • 7. Chapter 7: Testing
    • 7.1 Functional test suite
    • 7.2 Generators
    • 7.3 Business logic
      • 7.3.1 Happy path
      • 7.3.2 Empty cart
      • 7.3.3 Unreachable payment client
      • 7.3.4 Recovering payment client
      • 7.3.5 Failing orders
      • 7.3.6 Failing cart deletion
    • 7.4 Http routes
    • 7.5 Integration tests
      • 7.5.1 Resource allocation
      • 7.5.2 Postgres
      • 7.5.3 Redis
  • 8. Chapter 8: Assembly
    • 8.1 Logging
    • 8.2 Configuration
    • 8.3 Modules
    • 8.4 Resources
    • 8.5 Main
  • 9. Chapter 9: Deploying
    • 9.1 Docker image
      • 9.1.1 Optimizing image
      • 9.1.2 Run it locally
    • 9.2 Continuous Integration
      • 9.2.1 Dependencies
      • 9.2.2 CI build
      • 9.2.3 Furthermore
    • 9.3 Summary
  • 10. Chapter 10: Advanced techniques
    • 10.1 Tagless Final plugin
    • 10.2 MTL (Monad Transformers Library)
      • 10.2.1 Managing state
      • 10.2.2 Accessing context
    • 10.3 Classy optics
      • 10.3.1 Lenses
      • 10.3.2 Prisms
      • 10.3.3 Classy lenses
      • 10.3.4 Classy prisms
    • 10.4 Typeclass derivation
      • 10.4.1 Kinds
      • 10.4.2 Concrete types
      • 10.4.3 Higher-kinded types
      • 10.4.4 Higher-order functors
    • 10.5 Effectful streams
      • 10.5.1 Concurrency
      • 10.5.2 Resource safety
      • 10.5.3 Interruption

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