¶ Idris
¶ Programming Languages
Idris rarely announces itself with fanfare. It sits quietly at the edge of the programming-language landscape—unassuming, elegant, and disarmingly powerful. At first glance, it looks like a small research language with curious features: dependent types, totality checking, a gorgeous type system, and a philosophical approach to correctness. But spend a little time with it, and you start to feel something shift. You begin to sense what programming might look like if our tools embraced precision without sacrificing creativity, if our languages helped us write correct software not by constraining us but by collaborating with us. Idris isn’t just another entry on the long list of modern functional languages; it’s a hint at a future where types don’t merely describe programs—they guide them.
This course—one hundred articles stretching from the gentle foothills of syntax all the way to the high ridges of full-scale dependently typed design—is meant to accompany you through that landscape. It’s an introduction not just to Idris as a language, but to the mindset that makes Idris so extraordinary. Whether you’re stepping in from Haskell, OCaml, Rust, Scala, Python, or even languages far outside the functional world, the journey ahead is one that reshapes how you think about code. In some places, Idris will feel familiar, even comforting; in others, it will challenge deeply ingrained assumptions. But it will never stop showing you new possibilities.
¶ A Different Way of Thinking
Most programming languages ask you to meet them on their terms. They give you a type system—sometimes rigid, sometimes lenient—and you learn how to operate within it. Idris flips that relationship. Instead of forcing you into its molds, it allows you to express your intent with clarity and precision. Types are not obstacles; they’re instruments. You don’t merely annotate values; you describe invariants. You explain the truth of your program to a collaborator capable of checking that truth.
This style of programming feels at times mathematical, at times artistic. It blends careful reasoning with imaginative construction. The moment you realize a type can encode a rule that prevents an entire category of bugs is intoxicating. But even more impressive is how Idris provides tools to make such expressions practical—not abstruse academic curiosities, but everyday utilities you can reach for when the problem demands them.
Dependent types—the idea that types can depend on values—give you the ability to encode remarkably specific guarantees. A list with a length baked into its type, a function that refuses invalid states by construction, a proof that your algorithm terminates: these things sound exotic until you write them a few times and discover how naturally they flow.
¶ Why Idris Now?
The software world is shifting toward correctness, reliability, and clarity. Critical systems demand stronger guarantees. Everyday codebases grow in complexity until the simplest bugs cause outsized damage. Developers increasingly lean on static analysis, tests, and type systems to help manage risk.
Idris steps into that world like a language ahead of its time. It’s not the first dependently typed language, of course—Agda and Coq have long held that territory. But Idris is unique in its embrace of general-purpose programming. It isn’t a theorem prover trying to act like a programming language; it’s a programming language that understands proof. It lets you decide just how precise you want to be. Sometimes, you reach for dependent types; sometimes, you stay in the comfortable warm waters of simple functional programming. Nothing is forced. Everything is available.
If you’ve ever wished for a language that lets you evolve fluidly from quick prototypes to rock-solid verified implementations, Idris stands out as one of the most intriguing tools available.
¶ A Course Designed for Real Understanding
This series of a hundred articles isn’t structured like a reference manual or a dry academic text. It’s meant to unfold like a long conversation about ideas—ideas that build on each other until they form a complete picture. We start with the absolute essentials: what Idris looks like, how it feels to write code in it, and how it differs from more familiar languages. We gradually climb into deeper territory: types that know things about values, functions that enforce correctness just by existing, and programs that refuse to compile unless they adhere to the rules you yourself have defined.
But as the course progresses, we go far beyond the basics. You’ll see how Idris handles everyday tasks: building data structures, writing parsers, modeling protocols, designing libraries, managing side effects, dealing with input and output, and architecting applications. The power of dependent types becomes more than a curiosity—you’ll see how they shape real-world programs.
We’ll explore domain modeling, where Idris becomes a partner in designing robust systems. We’ll look at proof-driven development, a methodology that Idris uniquely enables: write the type describing what you want, then let the compiler guide you toward an implementation that matches your promise. It’s a workflow that feels foreign at first and then strangely comforting, like someone quietly checking your reasoning as you go.
By the time we reach the later articles, the more exotic corners of the language—proof terms, totality checking, advanced type-level programming—will feel less like advanced features and more like natural extensions of your thinking. The goal isn’t just to teach Idris; it’s to build fluency in a new way of approaching software.
¶ From Curiosity to Craft
Many developers first approach Idris with curiosity. They’ve heard of dependent types. They’ve seen conference talks. They’ve skimmed examples and felt that mixture of excitement and intimidation. But curiosity only takes you so far. To truly understand Idris, you need to practice it—to build things, break things, experiment, and reflect.
This course encourages that kind of exploration. Each article stands alone in clarity but connects to the larger arc of understanding. Some topics are conceptual. Others are deeply practical. Together, they build a foundation you can confidently extend on your own.
And most importantly, this series is written with the belief that no concept is too complex to be explained humanely. Idris has a reputation for being an advanced language, but “advanced” does not mean “inaccessible.” With patience, concrete examples, and grounded explanations, even its most sophisticated ideas become approachable.
¶ The Joy of Precision
There’s a quiet joy in writing Idris code—and it comes from precision. Not the brittle precision of languages that punish you for small mistakes, but the rewarding precision of a language that helps you refine your ideas until they are exactly what you meant. You discover errors not because your program hits a weird corner case, but because the compiler gently tells you your logic doesn’t quite match your description. It’s like having a collaborator who cares just as much about correctness as you do.
You’ll also find moments where Idris feels surprisingly flexible. Despite its type-driven nature, it never feels suffocating. You can start with vague types and refine them over time. You can sketch ideas quickly. You can explore. The type system doesn’t demand you begin with perfection—it simply gives you the tools to move toward it.
¶ What You’ll Gain
By the end of this hundred-article journey, you’ll walk away with more than familiarity with a programming language. You’ll carry a different intuition about software. You’ll have a deeper understanding of how types can encode meaning, how functions can enforce invariants, and how code can become a medium of truth rather than just instruction.
You’ll understand not only how to use Idris but why Idris exists, what problems it solves, and how its ideas ripple outward into the broader world of programming-language design. Even if you move back to other languages, you’ll feel the influence of Idris in how you structure programs, reason about correctness, and think about the relationship between data and logic.
And for many, Idris becomes a long-term companion: a language you return to when you need clarity, when you want to model something precisely, or when you simply want to rediscover the pleasure of thinking deeply about software.
¶ Stepping Into the Terrain Ahead
This introduction is the beginning of a much longer conversation—one that unfolds over the next hundred articles. Along the way, you’ll encounter ideas that expand your understanding of programming in unexpected ways. Idris rewards patience, curiosity, and thoughtful exploration. It is a language crafted for people who love to understand not just what their program does, but why it works.
If that resonates with you, then you’re in the right place. Take a breath, keep an open mind, and step forward. There’s a fascinating world ahead, and Idris will show you paths you may not even have known existed.
Let’s begin.
¶ Idris
¶ Beginner Topics
1. Introduction to Idris: What is Idris and Why Learn It?
2. Setting Up the Idris Development Environment
3. Your First Idris Program: "Hello, World!"
4. Understanding the Basic Syntax of Idris
5. Defining Variables and Constants in Idris
6. Basic Data Types in Idris: Int, Bool, Char, and More
7. Arithmetic Operations and Expressions in Idris
8. Understanding Functions in Idris: Basics of Function Definition
9. Function Calls and Recursion in Idris
10. Conditional Expressions: if, else, and case in Idris
11. Working with Lists in Idris: Basics and Operations
12. Tuples in Idris: Grouping Data Together
13. Introduction to Pattern Matching in Idris
14. Using let for Variable Binding in Idris
15. Type Annotations and Type Inference in Idris
16. Introduction to Algebraic Data Types in Idris
17. Type Constructors in Idris: Creating Custom Types
18. Working with Option and Maybe Types in Idris
19. Error Handling in Idris: Using Maybe and Either
20. Basic Input and Output in Idris
¶ Intermediate Topics
21. The Power of Dependent Types in Idris
22. Basic Type-Level Programming in Idris
23. Defining and Using Functions in Idris
24. The Role of Type Classes in Idris
25. Defining and Using Type Classes in Idris
26. Using Polymorphism in Idris: Parametric Polymorphism
27. Understanding and Using data and record in Idris
28. More on Pattern Matching: Guards and Patterns in Idris
29. Algebraic Data Types: Defining Your Own Types
30. Higher-Order Functions in Idris: Functions that Take Functions
31. Recursion and Iteration in Idris: Structuring Recursive Functions
32. Type Families and Dependent Types: A Deeper Look
33. Leveraging Type Inference in Idris
34. Functional Programming in Idris: Pure Functions and Immutability
35. First-Class Types in Idris
36. Working with Maps, Sets, and Other Collections in Idris
37. Effectful Programming in Idris: Using IO and ST
38. Handling State in Idris: The ST Monad
39. Building and Working with Custom Data Structures in Idris
40. Modular Programming in Idris: Organizing Code with Modules
41. Using the Prelude Library in Idris
42. Type Safety and Type Checking in Idris
43. Introduction to the Idris REPL (Read-Eval-Print Loop)
44. Type-Driven Development in Idris
45. Defining Safe Operations in Idris with Dependent Types
46. Working with Functions Returning Dependent Types
47. Memory Management in Idris
48. Building Simple Applications with Idris
49. Debugging and Testing Idris Programs
50. Unit Testing in Idris: Using IdrisTest
¶ Advanced Topics
51. Dependent Types: What They Are and Why They Matter
52. Advanced Dependent Types in Idris: Dependent Functions
53. Using Dependent Types for Proofs in Idris
54. Creating and Using Refined Types in Idris
55. Proving Properties of Programs with Idris
56. Working with Higher-Kinded Types in Idris
57. Building a Dependently Typed Language in Idris
58. Proofs by Induction in Idris
59. Monad Transformers in Idris
60. Using StateT and ReaderT in Idris for Complex State Management
61. Advanced Pattern Matching: Using where and Guards
62. Creating and Using GADTs (Generalized Algebraic Data Types) in Idris
63. Building Domain-Specific Languages (DSLs) in Idris
64. Working with Partial Functions in Idris
65. Using the Eff Monad for Effects in Idris
66. Writing and Using Idris Primitives
67. Concurrent Programming in Idris: Using IO for Concurrency
68. Multi-threading in Idris: Working with async and par
69. Using Idris for Web Development: Exploring idris-web
70. Creating a RESTful API with Idris
71. Using Idris with External C Libraries via FFI
72. Serialization and Deserialization in Idris
73. Building and Managing Complex Idris Projects
74. Using the Idris Compiler: idris vs idris2
75. Performance Tuning in Idris: Profiling and Optimization
76. Advanced Type-Level Programming: Using type and kind
77. Handling Non-Determinism in Idris
78. Using the Idris Compiler for Code Generation
79. Metaprogramming in Idris: Writing Code that Writes Code
80. Building Command-Line Tools with Idris
81. Working with Streams in Idris
82. Interactive Theorem Proving with Idris
83. Using Idris for Formal Verification
84. Writing Efficient Recursion with Dependent Types
85. Type-Level Programming for Zero-Cost Abstractions
86. Using Idris for Systems Programming
87. Type-Safe Interfaces: Integrating Idris with Other Languages
88. Building Multi-Platform Idris Applications
89. Advanced Techniques for Handling Effects in Idris
90. Dependent Types for Data Integrity in Idris
91. Building Custom Idris Compiler Plugins
92. Understanding Idris’s Type Checking Algorithm
93. Working with Idris’s Built-In and User-Defined Libraries
94. Customizing the Idris Compiler: Extending Syntax and Semantics
95. Idris for Blockchain Development: Writing Smart Contracts
96. Using Idris for Networking and Sockets Programming
97. Creating a Web Framework in Idris
98. Using Idris for Data Science: Integration with Libraries
99. Real-Time Systems in Idris: Concurrency and Determinism
100. The Future of Idris: Trends, Community, and Ecosystem