From: jeremy Ruten <jeremy.ruten@...>
Date: 2010-08-02T12:22:57+09:00
Subject: Re: Lazy array

Ruby 1.9 has the Enumerator class, which can act like a lazy list I
think. A good example is given in the documentation:

  fib = Enumerator.new { |y|
    a = b = 1
    loop {
      y << a
      a, b = b, a + b
    }
  }

  p fib.take(10) #=> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Also, this is a nice trick:

  Infinity = 1.0/0

  range = 5..Infinity
  p range.take(10) #=> [5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

This one only works for consecutive values though.

jeremy

On Sun, Aug 1, 2010 at 8:56 PM, skim <skim.la@gmail.com> wrote:
> Ruby Arrays dynamically expand as needed.  You can apply blocks to them to
> return things like even numbers.
>
> array = []
> array.size # => 0
> array[0] # => nil
> array[9999] # => nil
> array << 1
> array.size # => 1
> array << 2 << 3 << 4
> array.size # => 4
>
> array = (0..9).to_a
> array.select do |e|
>  e % 2 == 0
> end
>
> # => [0,2,4,6,8]
>
> Does this help?
>
> On Sun, Aug 1, 2010 at 17:45, Andrew Wagner <wagner.andrew@gmail.com> wrote:
>
>> How can I get a lazy array in Ruby? E.g., in Haskell, I can talk about
>> [1..], which is an infinite list, lazily generated as needed. I can also do
>> things like "iterate (+2) 0", which applies whatever function I give it to
>> generate a lazy list. In this case, it would give me all even numbers.
>> Anyway, I'm sure I can do such things in Ruby, but can't seem to work out
>> how.
>>
>