From: Eric Armstrong <Eric.Armstrong@...>
Date: 2006-07-22T22:05:48+09:00
Subject: Re: recursion in scripts -- global variables required?

Justin Collins wrote:
> Eric Armstrong wrote:
 >
>> Recursion is only being used to restart the
>> timer after it expires. No stack space is
>> required. Any sufficiently optimizing compiler
>> will take the stack out of the equation.
>> (Whether ruby does so is another matter.)
> 
> It doesn't, sadly. Soon, hopefully.
> 
Good to know. Thanks for the info.

Nice O-O solution below, too. (Too much scripting
in my blood.)

> I would think, given Ruby's nature, that the solution would be to create 
> a timer object. ;)
> 
> class MyTimer
> 
>        def initialize(hours, minutes, seconds)
>                @hours = hours
>                @minutes = minutes
>                @seconds = seconds
>        end
> 
>        #Rather than recursion, which in Ruby
>        #will eventually run out of stack space
>        def start
>                loop do
>                        run
>                end
>        end
> 
>        #Using nearly your exact same method
>        def run
>                #Won't see count down until the end without this
>                $stdout.sync = true
>                               #Your line breaks meant that 
> time_remaining was always zero
>                time_remaining = (3600 * @hours) + (60 * @minutes) + 
> @seconds
>                puts "sleeping for " + time_remaining.to_s
>                time_remaining.downto(0) do |i|
>                        sleep(1)
>                        print i.to_s + ".."
>                end
>                puts
>                beep; beep; beep
>                sleep 1
>                beep; beep; beep
>                sleep 1
>                beep; beep; beep
>        end
> end
> 
> timer = MyTimer.new(0,0,15)
> timer.start
> 
> 
> Maybe that helps...
> 
> -Justin
> 
>> As the mathematician said...
>>
>>   "It is now obvious that...wait a minute...
>>    let me check that...(works furiously)...
>>    Yes! It /is/ obvious..."
>>
>>
>> Matthew Smillie wrote:
>>> On Jul 20, 2006, at 20:03, Eric Armstrong wrote:
>>>
>>>> Is it me, or is it pretty much impossible
>>>> to write a recursive script in ruby unless
>>>> you use global variables?
>>>>
>>>> I have a simple countdown timer. I
>>>> set up the number of seconds to sleep,
>>>> sleep for a while, and then beep.
>>>>
>>>> A single run is easily done in a script
>>>> (code below). The problems start when
>>>> I define a run method and recurse.
>>>>
>>>> Unless I use global variables, there
>>>> doesn't seem to be any way for the
>>>> variables to get the data.
>>>>
>>>> Is that about it?
>>>
>>> Well, in this case, if you're using global variables, there's not 
>>> much of a point to making the method recursive (which stores all of 
>>> its local variables on the stack).  The typical way to do recursive 
>>> method is to pass the relevant information as parameters, e.g.,
>>>
>>> def countdown(seconds)
>>>   sleep(1)
>>>   puts "tick"
>>>   sleep(1)
>>>   puts "tock"
>>>   countdown(seconds - 2)
>>> end
>>>
>>> I'll also mention that a deep recursion like this is a horribly 
>>> inefficient way to do a countdown timer.
>>>
>>> matthew smillie
>>>
>>>>
>>>>
>>>> Initial Script
>>>> --------------
>>>> #!/usr/bin/env ruby
>>>>
>>>> # Beeps and character I/O
>>>> require 'curses'
>>>> include Curses
>>>>
>>>> @seconds = 10
>>>> @minutes = 0
>>>> @hours = 0
>>>>
>>>> #def run
>>>>   timeremaining = (3600 * @hours)
>>>>                 + (60 * @minutes)
>>>>                 + @seconds
>>>>   puts "sleeping for " + time_remaining.to_s
>>>>   timeremaining.downto(0) do |i|
>>>>     sleep(1)
>>>>     print i.to_s + ".."
>>>>   end
>>>>   puts
>>>>   beep; beep; beep
>>>>   sleep 1
>>>>   beep; beep; beep
>>>>   sleep 1
>>>>   beep; beep; beep
>>>>
>>>> # run
>>>> #end
>>>>
>>>> #run
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>