Stages
------

A gem for creating data pipelines out of tiny, reusable objects

Initial code stolen shamelessly from http://pragdave.blogs.pragprog.com/pragdave/2008/01/pipelines-using.html

Announcement blog post is at http://blog.igodigital.com/blog/on-recommendations/the-stages-gem

Usage
-----

You knit your stages together with '|'.  The leftmost pipeline stage will contain a generator, which usually is an infinite loop.  

Example
-------

Image you wanted to output every even number divisible by 3.  First you would need a class that would output even numbers.  Then you would want to select the ones that are divisible by 3.  A simple implementation using stages would like this

```ruby
pipeline = Evens.new | Select.new{ |x| x % 3 == 0}
loop { puts pipeline.run }
```

We have included some general purpose stages, map and select, which can accomplish many pipeline operations:

```ruby
pipeline = Evens.new | Map.new{ |x| x * 3} | Select.new{ |x| x % 7 == 0}
3.times{ pipeline.run } #[0, 42, 84]}
```

As of 0.2.7, we have a fancy new alternative syntax for this, which feels more like ruby:
```ruby
pipeline = evens | map{|x| x*3} | select{|x| x % 7 == 0}
```
Just include Stages::Sugar to get all the helpers.

Writing New Stages
------------------

If you are writing a stage that needs to process an element, you probably want to subclass Stage and implement handle_value.

If you are writing a generator, you probably want to subclass Stage and implement process

Stern Warnings
--------------

There are BREAKING CHANGES in 0.4.0.  Nil and false no longer kill pipelines, there is a special value that does that.  If you are overriding process and have a construct like this:
```ruby
while v = input
  do_things v
end
```

You will need to replace it with something like this:
```ruby
while !source_empty?
  do_things input
end
```
But, your pipelines now treat nil and false as perfectly valid values.  It's breaking, but it's probably an improvement.