This is an interpreter for Monkey, a programming language and interpreter from the book Writing an Interpreter in Go.
Here is a small example of Monkey.
let five = 5;
let ten = 10;
let add = fn(x, y) {
x + y;
};
let result = add(five, ten);
The code for this interpreter I have entered as I worked through the book, but I've also made small refactorings which helped me to understand it better. For the original source, please refer to the book.