From: Clemens Hintze <c.hintze@...>
Date: 2001-10-14T17:43:20+09:00
Subject: [ruby-talk:22508] ANN: Generator -- a class supporting lazy evaluation (Re: Open-ended  ranges)

Robert Feldt wrote:

(...)

> Ruby doesn't have infinite or unbounded data (by default) structs so what
> should this mean? We would have to add Inf (might be good for other
> situations) and introduce Object#default_max_value, but how to handle
> 
> (1..).to_a
> 
> without going for lazy evaluation?

(...)

Robert,

sorry for mis-using your post, but the opportunity is too nice to let
it pass :-)

There is a new class in town ... Generator. Generator is a class that
supports you to execute associated code blocks only partially by
suspending itself while returning an result to the caller.


Suspending means, that the whole state of the code block will be
stored in a
Continuation instance. Next invocation of a Generator instance will
back up where it
was left previously, ready to compute and return another value when
suspending again.

Code could looks like this:


   arr = ["Ruby", "Chan", "rules"]

   igen = Generator.new { arr.each { |el| suspend el } }

   puts igen.next      #-> Ruby

   puts igen.next      #-> Chan

   puts igen.next      #-> rules


The more comprehensive documentation is stored together with the
source code in RD format.
Let me know, if you like this gimmick or, of course, if you find any
errors!

You may obtain it from RAA:

   http://www.ruby-lang.org/en/raa-list.rhtml?name=Generator


Much fun,
\cle