Mini-rust in Rust 037: Complex expressions in mutation statements

Mini-rust in Rust 037: Complex expressions in mutation statements
Mini-rust in Rust 036: Evaluating code blocks
Mini-rust in Rust 035: Tidying up the evaluator
Mini-rust in Rust 034: Our first program, actually working
Mini-rust in Rust 033: Evaluating operators like += and *=
Mini-rust in Rust 032: Supporting a Unit type and type checking mutations
Mini-rust in Rust 031: Getting "while" through the type checker
Mini-rust in Rust 029: Parsing plus-equals
Mini-rust in Rust 028: Lexing plus-equals
Mini-rust in Rust 027: Parsing blocks of code