This is a compiler for the Monkey programming language written in Rust
Monkey has a C-like syntax, supports variable bindings, prefix and infix operators, has first-class and higher-order functions, can handle closures with ease and has integers, booleans, arrays and hashes built-in.
Official site is: https://monkeylang.org/. It's has various implementation languages :).
There is a book about learning how to make an interpreter: Writing An Interpreter In Go. This is where the Monkey programming language come from.