interesting. in ruby:

  ra:~$ irb
  irb(main):001:0> defined? a
  => nil
  irb(main):002:0> defined? b
  => nil
  irb(main):003:0> a = b
  NameError: undefined local variable or method `b' for   main:Object
  	from (irb):3
  irb(main):004:0> a
  => nil
  irb(main):005:0> b
  NameError: undefined local variable or method `b' for   main:Object
  	from (irb):5
  irb(main):006:0> defined? a
  => "local-variable"
  irb(main):007:0>

'a' gets defined.