A quick and easy-to-understand implementation of the `goto` directive in Ruby. Just wanted to prove that you can have goto in Ruby.

goto_in_ruby.rb

class Object
  HASH = {}

  def label(name, &block)
    HASH[name] = proc(&block)
  end

  def goto(name)
    raise "No label with name #{name} found" unless HASH.key?(name)

    HASH[name].call
  rescue LocalJumpError
    puts '[ERROR]: Local jump instructions such as `yield` `return` and `break` are not allowed in `label` blocks.
Read more at https://ruby-doc.org/core-2.5.0/LocalJumpError.html'
    exit(1)
  end

  def label_stack_main
    raise 'Usage of labels should be done within a block provided to "label_stack"' unless block_given?

    yield
    goto :start
  end
end

class InfiniteLoopStopper
  class << self
    def create_stop_label!
      label :stop_infinite_loop do
        puts 'I just jumped inside a class and stopped loop execution :D'
        goto :outside_loop
      end
    end
  end
end

def testing_function
  label(:infinite_loop) do
    (1..10**1000).each do |x|
      puts x
      goto :stop_infinite_loop if x == 1_578_216 # arbitrary number to prove control flow
    end
  end

  label(:outside_loop) do
    loop do
      puts 'One-time message'
      break # but local `breaks` are allowed :)
    end

    puts 'Phew, thought I will be looping forever'

    exit(0) # `return` and `break` are not allowed inside `label`
  end

  puts 'Code outside of labels will always be executed first :)'
end

require 'pry'

label_stack_main do
  label(:start) do
    InfiniteLoopStopper.create_stop_label! # you can create labels inside labels via function/class calls!
    testing_function

    puts 'Gonna loop 10^1000 times, please wait.. :)'

    goto :infinite_loop
  end
end

output.txt

Code outside of labels will always be executed first :)
Gonna loop 10^1000 times in 10 seconds, please wait.. :)
top label executed last
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
... # skipping some lines to make this more readable :)
1578208
1578209
1578210
1578211
1578212
1578213
1578214
1578215
1578216
I just jumped inside a class and stopped loop execution :D
One-time message
Phew, thought I will be looping forever