From: Simen <toalett@...>
Date: 2006-05-24T00:21:02+09:00
Subject: Re: How to "go to" in a RUBY script . . .

Leslie Viljoen wrote:
> On 5/23/06, Simen <toalett@gmail.com> wrote:
> 
>> There's also continuations. They're not only for web frameworks, you
>> know. It's fairly easy to write something goto-like with continuations.
>> I once did, for fun. You could do stuff like
>>
>>   label :loop
>>     [code]
>>   goto :loop
>>
> 
> As I understand it, continuations seem like blocks where all the local
> (instance) variables are automatically "static" (to use C's word). So
> you can go back to execute that block again at any time from anywhere
> and it's previous state is intact. Is that right?

Continuations represent "the rest of your program", or the 
*continuation* of a program from a point in code. So, when you do

  callcc do |continuation|
    continuation.call
  end
  puts "..."

All you're gonna see is "..." because that's the rest of the program. 
It's kinda like a superset of a closure: both the closure and the 
instruction pointer in one. What's happening in the code I posted is 
that the label method stores the continuation in a hash in a constant 
somewhere, and the goto method fetches the continuation and calls it.

Anyway, back to your regularly scheduled goto-bashing.

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