Lean is a functional programming language that makes it easy to write correct and maintainable code. You can also use Lean as an interactive theorem prover. Lean programming primarily involves defining types and functions. This allows your focus to remain on the problem domain and manipulating its data, rather than the details of programming. Lean has numerous features, including: - Type inference - First-class functions - Powerful data types - Pattern matching - Type classes - Extensible syntax - Hygienic macros - Dependent types - Metaprogramming framework - Multithreading - Verification: you can prove properties of your functions using Lean itself