A self-study curriculum for computer scientists who know PL theory and want to mechanize proofs in Lean 4 — from syntax to soundness of the Hindley-Milner type system.

Structure

├── README.md                          ← this file
├── tutorial-01-basics/                ← Lean 4 fundamentals
│   ├── 01-types-and-functions.md
│   ├── 02-inductive-types.md
│   ├── 03-propositions-and-proofs.md
│   ├── 04-quantifiers-and-equality.md
│   ├── 05-advanced-tactics.md
│   ├── 06-structures-type-classes.md
│   └── 07-dependent-types.md
├── tutorial-02-semantics/             ← PL semantics in Lean
│   ├── 08-syntax-representation.md
│   ├── 09-substitution.md
│   ├── 10-small-step-semantics.md
│   ├── 11-stlc-type-system.md
│   ├── 12-type-safety.md
│   ├── 13-hm-declarative.md
│   ├── 14-algorithm-w.md
│   └── 15-soundness-completeness.md
└── references.md                      ← all cited resources

How to Use

Install Lean 4 (VS Code + lean4 extension): lean-lang.org/lean4/doc/quickstart.html
Start with Tutorial 1, Unit 1. Each unit is a standalone .md file with inline Lean exercises.
Type the exercises into a .lean file and make it compile.
After Tutorial 1, move to Tutorial 2 to mechanize STLC and HM.

Prerequisites

Functional programming (Haskell/OCaml familiarity)
Basic PL theory (lambda calculus, operational semantics, type systems)
No prior proof assistant experience required

References

See references.md for the full list of resources.