From: "Peña, Botp" <botp@...>
Date: 2007-09-19T11:51:02+09:00
Subject: Re: Variable / Method Ambiguity

From: 7stud -- [mailto:dolgun@excite.com] 
# In ruby, for loops and if clauses don't create a scope.

irb(main):001:0> if false
irb(main):002:1>    x
irb(main):003:1> end
=> nil
irb(main):004:0> x
NameError: undefined local variable or method `x' for main:Object
        from (irb):4
irb(main):005:0> if false
irb(main):006:1>    x = 5
irb(main):007:1> end
=> nil
irb(main):008:0> x
=> nil

they can introduce a var (under the existing local scope of course).
i think its in the assignment behaviour if you look at it.  parser sees assignment even if code is not executed.
ruby just try to be friendly, but you can be sloppy if you want to and ruby will not give you an error :)
again, i think this is a faq.

kind regards -botp