From: MenTaLguY <mental@...>
Date: 2006-02-23T14:55:48+09:00
Subject: Re: [ANN] lazy.rb 0.9.5 -- transparent futures!

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On Thu, 2006-02-23 at 13:21 +0900, Daniel Nugent wrote:
> However, currently, there IS a block parameter (that of the promise
> itself, something to do with circular programming, which sounds
> intriguing, but I have hella no idea what it means [PLEASE SEND
> LINKS]), but it doesn't seem like you'd use it in most cases.

Here are a couple trivial examples...

Building a circular data structure (a linked list in this case):

 def build_circular_list( *stuff )
  promise { |result|
    if stuff.empty?
      nil
    else
      list =3D result
      stuff.reverse.each { |thing|
        list =3D [ thing, list ]
      }
      list
    end
  }
 end

Padding lines of text to a maximum width in a single pass:

 def pad_lines( lines )
   promise { |result|
     max_width =3D 0
     padded_lines =3D []

     lines.each { |line|
       max_width =3D line.length if line.length > max_width
       padded_lines.push promise { "%*s" % [ result[1], line ] }
     }

     [ padded_lines, max_width ]
   }[0]
 end

-mental

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