From: Eric Armstrong <Eric.Armstrong@...>
Date: 2006-07-21T06:42:50+09:00
Subject: Re: recursion in scripts -- global variables required?

There is no inefficency here. Recursion isn't
being used to count down. That's in a loop.

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.)

The question is really about the nature of
instance variables in a script, I guess.

It seems they can only be initialized in a
method. (Something I keep forgetting. I'm
/so/ used to intializing instance variables
in Java.)

Defining initialize() didn't work, because
the Object object the variables belong to
in a script is already created when that
definition is processed. So it never runs.

The obvious solution (which occurs to me only
now) is to create an init() method, and
invoke it before the first call to run().

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
>>
>>
>>
>>
> 
>