Algebraic Effects with Ruby

test.rb

class WithEffect
  def initialize
    @list = ["Foo", "Bar", 42, "Baz"]
  end

  def process_item(item)
    throw(:item_not_string, 42) unless item.is_a?(String)

    puts item
  end

  def signal_handler
    lambda do |signal, b, alternative_proc|
      b.local_variable_set(:item, alternative_proc.call(signal))
      true
    end
  end

  def iterate(alternative_proc = ->(signal) { "ALTERNATIVE#{signal}" })
    @list.each do |item|
      signal = catch(:item_not_string) do
        process_item(item)
      end
      redo if signal && signal_handler.call(signal, binding, alternative_proc)
    end
  end
end

WithEffect.new.iterate