gistfile1.rb

# I want this method in ruby-core
def let
  yield
end

def fib(i)
  let do |n = 1, result = 0|
    if i == -1
      result
    else
      i, n, result = i - 1, n + result, n
      redo
    end
  end
end

puts fib(10) #=> 89