Pragmatic Type-Level Design (PTLD E-Book)
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Pragmatic Type-Level Design

Practical introduction into type-level programming: design principles, design patterns, methodologies, approaches

About the Book

Pragmatic Type-Level Design is a book about programming in types, about the discipline of Software Design, lifted onto the level of types, and type-level approaches useful in real practice.

This is my second fundamental book about Software Design, in addition to Functional Design and Architecture.

I aim to provide a well-written and well-structured source of knowledge about type-level design. I’m not only talking about type-level features but also providing a reasoning framework for making the narrative complete and comprehensive. The central philosophy of this book - pragmatism - is used to build a practice-first methodology on how to approach types and not drown in the related complexity. The type-level design is difficult on its own, type-level features in various languages are difficult as well, and there is no need to raise the learning bar even more.

The book will be useful for developers who want to start doing real things on the type level.

If you liked my FDaA book, you’ll find PTLD enlightening and insightful as well.

Book completion estimation: end of 2025

Book topics:

type-level design, type-level eDSLs, correctness, complexity of solutions, Inversion of Control and Dependency Injection, domain modeling, type-level functional interfaces, design of business logic, interaction with impure subsystems, application architectures & design patterns, testing

GitHub repo: Pragmatic-Type-Level-Design

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  • Categories

    • Software Engineering
    • Haskell
    • Functional Programming
    • Software Architecture
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About the Author

Alexander Granin
Alexander Granin

International speaker, researcher, author

Expert Haskell and C++ developer

Software architect, team lead

Haskell consultant

Author of the book "Functional Design and Architecture"

Table of Contents

  • Part I The basics of type-level software design
    • 1 Emergent type-level design
      • 1.1 Approaching the type-level design
        • 1.1.1 Types and values
        • 1.1.2 Pragmatic Type-Level Design
        • 1.1.3 Typed Forms diagrams
      • 1.2 The foreshadowing of type-level design
        • 1.2.1 Basics of generics
        • 1.2.2 Basics of type classes
        • 1.2.3 Design principles
        • 1.2.4 Basics of type-level literals
      • 1.3 Summary
    • 2 Use case: simple extensibility
      • 2.1 Extensibility
        • 2.1.1 Extensibility mechanisms
        • 2.1.2 Extensibility requirement
        • 2.1.3 Extension points
      • 2.2 Basically extensible application
        • 2.2.1 Type class interface
        • 2.2.2 Heterogeneous storage problem
        • 2.2.3 Valuefication and existentification
        • 2.2.4 Valuefied storage
        • 2.2.5 Existentified storage
      • 2.3 Summary
    • 3 Use case: genericity and customization
      • 3.1 Type-level genericity
        • 3.1.1 Empty ADTs
        • 3.1.2 Type applications
        • 3.1.3 Ordinary and specific kinds
        • 3.1.4 Custom type-level ADTs and kinds
        • 3.1.5 Type-level lists
      • 3.2 Type-level customization
        • 3.2.1 Case-driven design methodology
        • 3.2.2 Customizable type-level eDSL
      • 3.3 Summary
    • 4 Use case: enforcing correctness
      • 4.1 Correctness is about meaning
        • 4.1.1 Type-safe vs correct
        • 4.1.2 Type-level vs correct
      • 4.2 Static referential integrity
        • 4.2.1 Strengthening the domain model
        • 4.2.2 Static and volatile domain notions
        • 4.2.3 Static operational integrity
        • 4.2.4 Type-level validators
        • 4.2.5 Static structural integrity
      • 4.3 Summary
  • Part II Architecturing type-level applications
    • 5 Application architecture
      • 5.1 Approaching software architecture
        • 5.1.1 Architecture levels
        • 5.1.2 Double Usage Assessment practice
        • 5.1.3 Two applications, same architecture
      • 5.2 Application structure
        • 5.2.1 Layered architecture
        • 5.2.2 Project structure
        • 5.2.3 Organizing type-level code
        • 5.2.4 Application layer
      • 5.3 Summary
    • 6 Components design
      • 6.1 Static and dynamic domain models
        • 6.1.1 Separate type-level and value-level models
        • 6.1.2 Granular Type Selector design pattern
        • 6.1.3 Interpretation of static and dynamic models
        • 6.1.4 Static materialization
        • 6.1.5 Data Transfer Objects and serialization
      • 6.2 Two functional interfaces
        • 6.2.1 Properties of a true interfacing mechanism
        • 6.2.2 Type class versus Free monad
        • 6.2.3 Free monad interface
        • 6.2.4 Type class interface and the Dynamic Payload design pattern
      • 6.3 Summary
  • Part III Advanced type-level design
  • Part IV Rosetta Stone
  • Appendices
    • Appendix A Typed Forms diagrams
      • A.1 Typed Forms
        • A.1.1 General conventions
        • A.1.2 Regular types, pairs, aliases, lists
        • A.1.2 Simple ADTs
        • A.1.2 Parametrized types
        • A.1.2 Generics specification syntax
        • A.1.2 Type classes and instances
        • A.1.2 Kinds
        • A.1.2 Type promotion
        • A.1.2 Simple type families and the HKD template
    • Appendix D The Mythologized Correctness
      • D.1 Type safety
        • D.1.1 Generic type safety
        • D.1.2 Descriptive type safety
      • D.2 Technical correctness
        • D.2.1 Correctness of data structures and algorithms
        • D.2.2 Correctness of data models
        • D.2.3 Correctness of languages
        • D.2.4 Conclusion

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