DSL Example in Ruby

more_test_events.rb

def monthly_sales
  110 # TODO: read the real number from the database
end

setup do
  puts "Setting up target sales"
  @target_sales = 100
end

event "monthly sales are suspiciously high" do
  monthly_sales > @target_sales
end

event "monthly sales are abysmally low" do
  monthly_sales < @target_sales
end

redflag.rb

lambda {
  setups = []
  events = {}

  Kernel.send :define_method, :event do |name, &block|
    events[name] = block
  end

  Kernel.send :define_method, :setup do |&block|
    setups << block
  end

  Kernel.send :define_method, :each_event do |&block|
    events.each_pair do |name, event|
      block.call name, event
    end
  end

  Kernel.send :define_method, :each_setup do |&block|
    setups.each do |setup|
      block.call setup
    end
  end
}.call

Dir.glob('*events.rb').each do |file|
  load file
  each_event do |name, event|
    env = Object.new
    each_setup do |setup|
      env.instance_eval &setup
    end
    puts "ALERT: #{name}" if env.instance_eval &event
  end
end

test_events.rb

event "the sky is falling" do
  @sky_height < 300
end

event "it's getting closer" do
  @sky_height < @mountains_height
end

setup do
  puts "Setting up sky"
  @sky_height = 100
end

setup do
  puts "Setting up mountains"
  @mountains_height = 200
end