From: Robert Klemme <shortcutter@...>
Date: 2011-05-18T20:12:43+09:00
Subject: Re: Making fibers enumerable

On Wed, May 18, 2011 at 9:39 AM, Rahul Kumar <rahulsinner@gmail.com> wrote:
> Hi,
>
> Most of the `Enumerable` methods can be used for fiber based generators if
> `Fiber` is made enumerable.
>
> class Fiber
>  include Enumerable
>  def each
>    loop { yield self.resume }
>  end
> end
>
> def fib_gen
>  Fiber.new {
>    a, b = 0, 1
>    while true
>      Fiber.yield a
>      a, b = b, a + b
>    end
>  }
> end
>
> # Find the fibonacci number greater than 1000
> fib_gen.find {|x| x > 1000 }
> # take first 10 fibonacci numbers
> fib_gen.take 10
> # take_while numbers are smaller than 1000
> fib_gen.take_while {|x| x < 1000 }
>
> If it could be the default behavior, it would be very useful. Some methods
> won't be applicable, particularly for non-terminating generators in their
> default incarnation viz. drop_while. It can either be re-written to advance
> the generator using Fiber#resume or it can be left upto the user to handle
> infinite sequences correctly.
>
> If I understand correctly, writing generators was one of the purposes of
> fibers. Why can't fibers be made enumerable by default?

I am not sure how that interacts with the original intent of Fibers:
their main purpose is to bring coroutines to Ruby.

http://en.wikipedia.org/wiki/Coroutines

How would your example look if there was another generation that you
wanted to do concurrently?  Because for the single threaded generator
case there is already a tool: Enumerator.new.  The example in the
documentation even uses Fibonacci Numbers as example. :-)

http://www.ruby-doc.org/core/classes/Enumerator.html#M000299

fib_gen = Enumerator.new { |y|
  a = b = 1
  loop {
    y << a
    a, b = b, a + b
  }
}

Now you can do exactly the same as you did with your example

# Find the fibonacci number greater than 1000
fib_gen.find {|x| x > 1000 }
# take first 10 fibonacci numbers
fib_gen.take 10
# take_while numbers are smaller than 1000
fib_gen.take_while {|x| x < 1000 }

For this Fiber would be the wrong tool.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/