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Gentle Introduction to Dependent Types with Idris
Gentle Introduction to Dependent Types with Idris
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Gentle Introduction to Dependent Types with Idris

Last updated on 2019-06-17

About the Book

You can purchase a printed edition of this book on Amazon

Dependent types are a powerful concept that allows us to write proof-carrying code. Idris is a programming language that supports dependent types. We will learn about the mathematical foundations, and then write correct software and mathematically prove properties about it.

This book aims to be accessible to novices that have no prior experience beyond high school mathematics. Thus, this book is designed to be self-contained.

The reason for writing this book is that I could not find a book that explained how things work, so I had to do a lot of research on the internet through white-papers, forums, and example code in order to come up with a complete picture of what dependent types are and what they are good for.

The first part of this book serves as an introduction to the theory behind Idris, while the second part is a practical introduction to Idris with examples.

Contributions are welcome on GitHub.

About the Author

Boro Sitnikovski
Boro Sitnikovski

Boro Sitnikovski has 10+ years of experience working professionally as a Software Engineer. He started programming with the Assembly programming language on an Intel x86 at the age of 10. While in high school, he has won several prizes on competitive programming, varying from 4th, 3rd, and 1st place.

He has a Bachelor of Engineering in Informatics degree, and his thesis was titled “Programming in Haskell using algebraic data structures”. His research interests include: programming languages, mathematics, logic, algorithms, and writing correct software.

He is a strong believer in the open source philosophy, and contributes to various open source projects.

In his spare time he enjoys some time-off with his family.

Table of Contents

  • Preface and acknowledgments
  • Introduction
  • 1. Formal systems
    • 1.1. MU puzzle example
  • 2. Classical mathematical logic
    • 2.1. Hierarchy of mathematical logic and definitions
      • 2.1.1. Propositional logic
      • 2.1.2. First-order logic
      • 2.1.3. Higher-order logic
    • 2.2. Set theory abstractions
    • 2.3. Substitution and mathematical proofs
      • 2.3.1. Proofs by truth tables
      • 2.3.2. Three-column proofs
      • 2.3.3. Formal proofs
      • 2.3.4. Mathematical induction
  • 3. Type theory
    • 3.1. Lambda calculus
      • 3.1.1. Term reduction
    • 3.2. Lambda calculus with types
    • 3.3. Dependent types
    • 3.4. Intuitionistic theory of types
      • 3.4.1. Intuitionistic logic
  • 4. Programming in Idris
    • 4.1. Basic syntax and definitions
      • 4.1.1. Defining functions
      • 4.1.2. Defining and inferring types
      • 4.1.3. Anonymous lambda functions
      • 4.1.4. Recursive functions
      • 4.1.5. Recursive data types
      • 4.1.6. Total and partial functions
      • 4.1.7. Higher-order functions
      • 4.1.8. Dependent types
      • 4.1.9. Implicit parameters
      • 4.1.10. Pattern matching expressions
      • 4.1.11. Interfaces and implementations
    • 4.2. Curry-Howard isomorphism
  • 5. Proving in Idris
    • 5.1. Weekdays
      • 5.1.1. First proof (auto-inference)
      • 5.1.2. Second proof (rewrite)
      • 5.1.3. Third proof (impossible)
    • 5.2. Natural numbers
      • 5.2.1. First proof (auto-inference and existence)
      • 5.2.2. Second proof (introduction of a new given)
      • 5.2.3. Third proof (induction)
      • 5.2.4. Ordering
      • 5.2.5. Safe division
      • 5.2.6. Maximum of two numbers
      • 5.2.7. List of even naturals
      • 5.2.8. Partial orders
    • 5.3. Computations as types
    • 5.4. Trees
      • 5.4.1. Depth
      • 5.4.2. Map and size
      • 5.4.3. Length of mapped trees
  • Conclusion
  • Further reading
  • Appendix A: Writing a simple type checker in Haskell
    • Evaluator
    • Type checker
    • Environments
  • Appendix B: Metamath
  • Appendix C: IO, Codegen targets, compilation, and FFI
    • IO
    • Codegen
    • Compilation
    • Foreign Function Interface
  • About the author
  • Notes

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