When Ruby undefined becomes defined

gistfile1.rb

> irb
1.9.3p0 :001 > a 
NameError: undefined local variable or method `a' for main:Object
	from (irb):1
	from /Users/dnagir/.rvm/rubies/ruby-1.9.3-p0/bin/irb:16:in `<main>'
1.9.3p0 :002 > b
NameError: undefined local variable or method `b' for main:Object
	from (irb):2
	from /Users/dnagir/.rvm/rubies/ruby-1.9.3-p0/bin/irb:16:in `<main>'
1.9.3p0 :003 > a = b
NameError: undefined local variable or method `b' for main:Object
	from (irb):3
	from /Users/dnagir/.rvm/rubies/ruby-1.9.3-p0/bin/irb:16:in `<main>'
1.9.3p0 :004 > a = a
 => nil 
1.9.3p0 :005 > a
 => nil 

Here's the funny thing I wanted to fix in Ruby last year:

a = 1 if defined?(a)
=> 1

The thing is that if the engine sees you assign something to an unknown name, it assumes it's a variable and places it in the var table. When it later checks for whether it's defined, it sees the name in the var table and the condition becomes true. Ideally, they should have either skipped analyzing the code inside the conditional block, or placed var names in temporary table that is merged with the main one if the condition is true.

Another good one.
I think I did come around that too.

Ruby makes me scratch my head pretty often :)