Iteration is a control-flow technique in which a method call is supplemented with code the method can execute during its own operation. Unlike conditional execution, it can pass control between the method and that code. section 6.0 section 6.3
In Ruby, an iterator is a method that expects a code block. The method can execute that block; inside your own iterator, use `yield` to call it. The block and `yield` are the core ingredients of iteration. section 6.3.1
loop { puts "Looping forever!" }
This block is passed to `loop`, which repeatedly executes its code. section 6.3.1
