fibonacci recursive function for Ruby

fibonacci.rb

=begin
# mruby doesn't have the even? method.
class Integer
  def even?
    self % 2 == 0
  end
end
=end

def trcall(value)
  while value.instance_of?(Proc)
    value = value.call
  end
  value
end

def fib(n)
  trcall(fib_iter(1, 0, 0, 1, n))
end

def fib_iter(a, b, p, q, count)
  return b if count.zero?
  if count.even?
    np = p**2 + q**2
    nq = 2*p*q + q**2
    nc = count.div(2)
    proc {fib_iter(a, b, np, nq, nc)}
  else
    na = b*q + a*q + a*p
    nb = b*p + a*q
    nc = count - 1
    proc {fib_iter(na, nb, p, q, nc)}
  end
end

# 100.upto(110){|i| puts fib(i)}