p = proc do |arg|
      return if arg == 17
      puts arg
    end

    p[1]  # prints "1"
    p[17] # prints nothing

    p = Proc.new do |arg|
      return if arg == 17
      puts arg
    end

    p[1]  # prints "1"
    p[17] # raises LocalJumpError

Thanks!
-=R
from http://rubyforge.org/tracker/index.php?func=detail&aid=17623&group_id=426&atid=1698