Kleisli Gem is pretty awesome

kleisli.rb

require 'kleisli'

def do_lots(count)
  (0..count).reduce(0){|sum, value| sum + value }
end

future = Future(100000000) >-> value {
  Future { 
    do_lots(value.call)
  } >-> big_sum {
    Future{ big_sum.call }
  }
}

puts "I'm doing other stuff."

puts "Oh, let's also add 7"
future2 = future >-> value {
  Future{ value.call + 7 }
}

puts future2.await

# => I'm doing other stuff.
# => Oh, let's also add 7
# => 5000000050000007