From: MenTaLguY <mental@...>
Date: 2005-11-07T20:54:52+09:00
Subject: lazy fibs

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I've been playing around with adding explicit support for lazy streams
to lazy.rb.  Even without explicit support, though, lazy streams aren't
hard.  Check this out:

 require 'lazy'

 def generate( &f )
   promise { f.call( generate( &f ) ) }
 end

 def head( pair ) ; pair[0] ; end

 def tail( pair ) ; pair[1] ; end

 def fibs
   state =3D [ 1, 0 ]
   generate { |rest|
     value =3D state[0] + state[1]
     state[0] =3D state[1]
     state[1] =3D value
     [ value, rest ]
   }
 end

 blah =3D fibs
 20.times do
   p head( blah )
   blah =3D tail( blah )
 end

Nifty, huh?

-mental

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