argh.rb

module ExecutionMethods
  def curry_one x
    curry[x].extend ExecutionMethods
  end

  alias :to       :curry_one
  alias :on_event :curry_one
  alias :on       :curry_one
end

class Execution < Proc
  include ExecutionMethods
end

class Expectation < Proc
  alias :to :call
end

def expect object
  Expectation.new do |exec|
    exec.call object
  end
end

def transition_from from
  Execution.new do |to, event, on, thing|
    p [from, to, event, on, thing]
  end
end

multiple = Object.new
expect(multiple).to transition_from(:standing).to(:walking).on_event(:walk).on(:move)