GoldyLox: an interpreter for Lox, written in Ruby

I'm following along with Robert Nystrom's Crafting Interpreters to learn how to write an interpreter (which still seems magical to me), as well as to learn (more) Ruby and RBS.

Showcase

Below are a couple of examples to where the Ruby code is just so much more elegant and beautiful than Java.

These put a smile on my face when I wrote them. 😍

Scanning until the end of the line or file

while (peek() != '\n' && !isAtEnd()) advance();

advance until peek == "\n" || eof?

The Ruby code reads just almost like plain English. Swapping while with until to flip the condition makes it crystal clear.

Resolving a variable's depth

private void resolveLocal(Expr expr, Token name) {
  for (int i = scopes.size() - 1; i >= 0; i--) {
    if (scopes.get(i).containsKey(name.lexeme)) {
      interpreter.resolve(expr, scopes.size() - 1 - i);
      return;
    }
  }
}

def resolve_local(expr, name)
  @scopes.reverse_each.with_index do |scope, i|
    if scope.key? name.lexeme
      @interpreter.resolve(expr, i)
      return
    end
  end
end

Using reverse_each makes the intent immediately clear. There's also no need for scopes.get(i).

Replacing scopes.size() - 1 - i with just i avoids any chance for off-by-one errors.

Interpreting a call expressions

@Override
public Void visitCallExpr(Expr.Call expr) {
  resolve(expr.callee);
  
  for (Expr argument : expr.arguments) {
    resolve(argument);
  }
  
  return null;
}

def visit_call(expr)
  resolve expr.callee
  expr.arguments.each { resolve it }
end

I rest my case. ☺️