DG example: bind: following links on a Google search

dg_example_bind.rb

EM.run do
  fetch('http://google.com/search?q=deferrable_gratification').bind! do |doc|
    fetch((doc / 'ol' / 'li' / 'a')[0][:href])
  end.bind! do |doc|
    fetch((doc / '#repository_homepage').at(:a)[:href])
  end.callback do |doc|
    puts doc.at(:title).inner_text
    # now the previous 'doc's aren't in scope, so I can't accidentally
    # refer to them
  end.errback do |error|
    puts "Error: #{error}"
  end.bothback { EM.stop }
end

dg_example_nested_callbacks.rb

EM.run do
  fetch('http://google.com/search?q=deferrable_gratification').callback do |doc1|
    fetch((doc1 / 'ol' / 'li' / 'a')[0][:href]).callback do |doc2|
      fetch((doc2 / '#repository_homepage').at(:a)[:href]).callback do |doc3|
        puts doc3.at(:title).inner_text
        # I could also have mistyped 'doc3' as 'doc2' and got the wrong
        # behaviour, but no exception to flag it
      end.errback do |error|
        puts "Error finding homepage link: #{error}"
      end.bothback { EM.stop }
    end.errback do |error|
      puts "Error loading first search result: #{error}"
      EM.stop
    end
  end.errback do |error|
    puts "Error retrieving search results: #{error}"
    EM.stop
  end
end