From: Daniel Sheppard <daniels@...>
Date: 2004-04-08T15:59:40+09:00
Subject: Bug in Array.zip

This email from the ruby vs python discussion points out a bug in
Array.zip

> >> p=Prime.new
> => #<Prime:0x2b43048 @primes=[], @seed=1, @counts=[]>
> >> for i in [1,2,3].zip(p)
> >>  p i
> >> end
> TypeError: cannot convert Prime into Array
>         from (irb):5:in `zip'
>         from (irb):5
> >> p.kind_of?Enumerable
> => true
> 
> guess why you can't use a prime? because you can't pause the 
> yielding. You're forced to use the whole number of Prime 
> number that are actually.. infinite. So, you discover that 
> you can't zip it cause zip calls to_ary.

The following is a reimplementation of zip that does not use an
intermediate array. Performance-wise, it will probably suck due to the
use of continuations - perhaps the code in Array.zip should fall back to
something like this if it fails to convert the passed argument into an
array?

class Array
  def zip(otherArray)
    normalFlow, nextIter, value = nil
    callcc { |normalFlow|
      callcc { |nextIter| normalFlow.call }
      otherArray.each { |x|
        value = x
        callcc { |nextIter| normalFlow.call }
      }
      nextIter = nil
      normalFlow.call
    }
    collect { |first|
      [ first, 
        if nextIter 
          callcc { |normalFlow| nextIter.call }
          value
        end
      ]
    }
  end
end

(0..20).to_a.zip(Prime.new).each { |i|
  p i
}
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