a.rb

require './lib/lspace'

class << Fiber
  in_lspace :new
end

LSpace.with(x: 'wrapper') do
  f = LSpace.with(x: 'in fiber') do  
    Fiber.new do  

      puts "1 #{LSpace[:x]}" # in fiber
      Fiber.yield
      puts "3 #{LSpace[:x]}" # in fiber
    end
  end

  LSpace.with(x: 'in main') do
    f.resume

    puts "2 #{LSpace[:x]}" # in main

    LSpace.with(x: 'terminator') do
      f.resume
      puts "4 #{LSpace[:x]}" # terminator
    end
  end
end