handing undefined attributes in chef/ruby loops

custom resource definition.rb

chef:recipe > a = 'stuff'
chef:recipe >
chef:recipe > service 'testing_start' do
chef:recipe > action defined?(a) ? :start : :stop
chef:recipe ?> end
 => <service[testing_start] @name: "testing_start" @noop: nil @before: nil @params: {} @provider: nil @allowed_actions: [:nothing, :enable, :disable, :start, :stop, :restart, :reload] @action: [:start] @updated: false @updated_by_last_action: false @supports: {:restart=>false, :reload=>false, :status=>false} @ignore_failure: false @retries: 0 @retry_delay: 2 @source_line: "(irb#2):144:in `irb_binding'" @guard_interpreter: :default @elapsed_time: 0 @resource_name: :service @service_name: "testing_start" @enabled: nil @running: nil @parameters: nil @pattern: "testing_start" @start_command: nil @stop_command: nil @status_command: nil @restart_command: nil @reload_command: nil @init_command: nil @priority: nil @cookbook_name: nil @recipe_name: nil>
chef:recipe >
chef:recipe >
chef:recipe > d
'
NameError: No resource, method, or local variable named `d' for `Chef::Recipe ""'
	from /Library/Ruby/Gems/2.0.0/gems/chef-11.12.4/lib/chef/dsl/recipe.rb:49:in `rescue in method_missing'
	from /Library/Ruby/Gems/2.0.0/gems/chef-11.12.4/lib/chef/dsl/recipe.rb:44:in `method_missing'
	from (irb#2):149
chef:recipe >
chef:recipe > service 'testing_stop' do
chef:recipe > action defined?(d) ? :start : :stop
chef:recipe ?> end
 => <service[testing_stop] @name: "testing_stop" @noop: nil @before: nil @params: {} @provider: nil @allowed_actions: [:nothing, :enable, :disable, :start, :stop, :restart, :reload] @action: [:stop] @updated: false @updated_by_last_action: false @supports: {:restart=>false, :reload=>false, :status=>false} @ignore_failure: false @retries: 0 @retry_delay: 2 @source_line: "(irb#2):151:in `irb_binding'" @guard_interpreter: :default @elapsed_time: 0 @resource_name: :service @service_name: "testing_stop" @enabled: nil @running: nil @parameters: nil @pattern: "testing_stop" @start_command: nil @stop_command: nil @status_command: nil @restart_command: nil @reload_command: nil @init_command: nil @priority: nil @cookbook_name: nil @recipe_name: nil>
chef:recipe >