Code Walk Through

The REPL is the simplest part of the interpreter implementation. It uses the linefeed crate to implement the functionality.

The REPL first creates an instance of env to hold the global variables for the interpreter.

let mut env = Rc::new(RefCell::new(env::Env::new()));

The REPL is a simple while loop that takes one line as an input from the user, evaluates it, and prints out the evaluated object. The REPL is terminated if the user enters the exit keyword.

while let ReadResult::Input(input) = 
  			  reader.read_line().unwrap() {
    if input.eq("exit") {
    let val = eval::eval(input.as_ref(), &mut env)?;
    match val {
        Object::Void => {}
        Object::Integer(n) => println!("{}", n),
        Object::Bool(b) => println!("{}", b),
        Object::Symbol(s) => println!("{}", s),
        Object::Lambda(params, body) => {
            for param in params {
                println!("{} ", param);
            for expr in body {
                println!(" {}", expr);
        _ => println!("{}", val),