From: Josh Cheek <josh.cheek@...>
Date: 2011-01-22T16:12:36+09:00
Subject: Re: Lexical vs Dynamic Scope

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On Sat, Jan 22, 2011 at 12:20 AM, Tim Morgan <tim@timmorgan.org> wrote:

> Forgive this very basic question, but Googling has not answered my
> question, and I'm sure it's a simple one for the gurus here.
>
> I've been using Ruby for years, and I've always had questions about
> how it handles scope. Usually Ruby just does what I would expect it
> to.
>
> In reading about lexical vs. dynamic scope on various places on the
> Web, I read that Ruby has lexical (static) scope. But I cannot prove
> it to myself with code. For example, the following produces one (1) --
> not zero (0) as I would expect it to if Ruby was truly statically
> scoped:
>
> x = 0
> f = Proc.new { x }
> g = Proc.new {
>  x = 1
>  f.call
> }
> puts g.call
> # => 1
>
> (I purposely used Procs instead of regular methods here since Ruby
> methods cannot see the top-level "x" variable at all, which is a whole
> other issue.)
>
> Is Ruby really dynamically scoped?
>
>
The x in g is the same as the x outside of g. There is only one single x in
your program, so this doesn't show much. Maybe this instead?

def show_error(f)
  f.call
rescue => e
  e
end

f = lambda { x }
show_error f # => #<NameError: undefined local variable or method `x' for
main:Object>

x = 1
show_error f # => #<NameError: undefined local variable or method `x' for
main:Object>

g = lambda { x }
show_error g # => 1

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