Something like:

1.9.3-head :065 > b = a + 1

raises an exception if a is not defined:

NameError: undefined local variable or method `a' for main:Object
	from (irb):65
	from /home/tamara/.rvm/rubies/ruby-1.9.3-head/bin/irb:16:in `<main>'

Is there a more elegant way to check if a is defined besides wrapping
it in begin/rescue/end block? Something along the order of:

Object.defined?('a')

(I'm probably thinking about this wrong...)