LEANPROVER.GITHUB.IO

Lean is an interactive theorem prover developed at Microsoft Research, based on dependent type theory. Dependent type theory unites the worlds of programs and proofs; thus, Lean is also a programming language. Lean takes its dual nature seriously, and it is designed to be suitable for use as a general-purpose programming language-Lean is even implemented in itself. This book is about writing programs in Lean... When viewed as a programming language, Lean is a strict pure functional language with dependent types. A large part of learning to program with Lean consists of learning how each of these attributes affects the way programs are written, and how to think like a functional programmer. Strictness means that function calls in Lean work similarly to the way they do in most languages: the arguments are fully computed before the function's body begins running. Purity means that Lean programs cannot have side effects such as modifying locations in memory, sending emails, or deleting..