lazy fibs

[MenTaLguY]

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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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