Proof of non-local returns in Ruby

non_local_returns.rb

# Some of the tests for this fail, in a way that's surprising to Python users...
# Why?

class List
  def initialize(*elements)
    @elements = elements
    @elements.each do |e|
      return if e.nil?
    end
  end

  def handle_elements(&block)
    block.(@elements, &block)
  end

  def find_3_and_recursively_add_1_on_the_way_back_up
    handle_elements do |elements, &block|
      return unless elements.first
      if elements.first == 3
        return elements.first
      else
        block.(elements.drop(1), &block) + 1
      end
    end
  end
end

describe "blocks" do
  context "no elements" do
    let(:list) { List.new }

    it "returns nil" do
      list.find_3_and_recursively_add_1_on_the_way_back_up.should be_nil
    end
  end

  context "1 element" do
    context "no match" do
      let(:list) { List.new(2) }

      it "returns nil" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should be_nil
      end
    end

    context "that matches" do
      let(:list) { List.new(3) }

      it "returns one plus the element" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should eq 3
      end
    end
  end

  context "2 elements" do
    context "no match" do
      let(:list) { List.new(2, 4) }

      it "returns nil" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should be_nil
      end
    end

    context "match" do
      let(:list) { List.new(2, 3) }

      it "returns nil" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should eq 4
      end
    end
  end

  context "3 elements" do
    context "no match" do
      let(:list) { List.new(2, 4, 5) }

      it "returns nil" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should be_nil
      end
    end

    context "match" do
      let(:list) { List.new(1, 2, 3) }

      it "returns nil" do
        list.find_3_and_recursively_add_1_on_the_way_back_up.should eq 5
      end
    end
  end
end