From: Florian Gross <flgr@...>
Date: 2004-03-11T06:24:38+09:00
Subject: Re: Why there is no Continuation.new ?

gabriele renzi wrote:
> Hi gurus and nubys,

Moin!

> Btw, I wonder what's wrong with a more rubyish way to use
> continuations.

Nothing, it's just that we can't really use Continuation.new because 
standardized behavior would be to return only a single object: The newly 
created Continuation instance. (But that's quite useless.)

However I've got this code in a file named simplecc.rb:

def Continuation.create(*args, &block)
   cc = nil; result = callcc do |c|
     cc = c; block.call(cc) if block and args.empty?
   end
   result ||= args
   return *[cc, *result]
end

It's used like this:

# This example counts from 10 down to 0 using continuations
cc, counter = Continuation.create(10)
puts counter
cc.call(counter - 1) if counter > 0

# This implements inject using continuations
# Please note that this implementation isn't fully compatible with the
# original inject. (In order to keep it simple)
class Array
   def cc_inject(value = nil)
     copy = self.clone

     cc, result, item = Continuation.create(value, nil)
     next_item = copy.shift
     if result and item
       cc.call(yield(result, item), next_item)
     elsif next_item
       cc.call(next_item, result)
     end

     return result
   end
end
[1, 2, 3].cc_inject { |state, item| state + item } # => 6

Regards,
Florian Gross