From: Brian Candler <b.candler@...>
Date: 2009-01-19T18:04:12+09:00
Subject: Re: A stream implementation for Ruby

Robert Dober wrote:
> Streams are lazily evaluated lists.

Aside: it is also possible to make use of infinite enumerators in Ruby 
(i.e. a traditional 'each' method which yields an infinite number of 
values), and this may be sufficient in some applications.

In order for this to be useful, you need to process chains of methods 
acting 'horizontally' instead of 'vertically'. The block form of 
Enumerator lets this be done natively in ruby 1.9:
http://redmine.ruby-lang.org/issues/show/707

and with a little work, this can be made entirely transparent to map, 
select etc:
http://redmine.ruby-lang.org/issues/show/708

It turns out to be very easy to implement the block form of Enumerator 
in ruby 1.8. I contributed an implementation of this to the Facets 
project:

http://facets.rubyforge.org/git?p=facets.git;a=blob_plain;f=lib/lore/facets/enumerator.rb;hb=HEAD
http://facets.rubyforge.org/git?p=facets.git;a=blob_plain;f=lib/more/facets/filter.rb;hb=HEAD

Anyway, I just thought this was worth a mention. It's not as powerful as 
full lazy evaluation, although if you combine this with Generators I 
think it gets pretty close.

Regards,

Brian.
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