##</code><code>##

class Array
  def sieve (*how)
    call = block_given?
    slots = Hash[]

    how.push(Proc.new { true })
    how.each { |h| slots[h] = [] }

    self.each { |x|
      i = (call == true) ? yield(x) : x

      how.each { |h|
        if h.call(i) == true
          slots[h].push(x)
          break
        end
      }
    }

    return how.collect { |h| slots[h] }.flatten
  end
end

a = [6,5,2,4,3,1,7]
puts a.sieve(
  Proc.new { |n| n < 5 },
  Proc.new { |n| n < 10 }
) { |x| x * 2 }.inspect

##</code><code>##

sieve {block 1}.{block 2}.{block 3}.sift(array) {how}

##</code><code>##

this_sieve = sieve {b1}.{b2}.{b3}
# and then
this_sieve.sift(array) { how }