Lexical vs Dynamic Scope

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?

On Sat, Jan 22, 2011 at 12:20 AM, Tim M. [email protected] wrote:

not zero (0) as I would expect it to if Ruby was truly statically

(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

On Jan 22, 1:12am, Josh C. [email protected] wrote:

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?

Ahhh. I see. Thanks!

On Sat, Jan 22, 2011 at 4:12 AM, Josh C. [email protected]
wrote:

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

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

After doing the above, try this.

def x
“Anything returned by the (Receiver).x method”
end

show_error f # => “Anything returned by the (Receiver).x method”
show_error g # => 1

At compile time…
f = lambda { x }
x is not defined, and is thought to be a method!

Look…
http://www.ruby-forum.com/topic/724184

Abinoam Jr.

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