> Because I read some other lauguage said that recursive programming can
> totally replace loop structure.
> So I want to think the loop as the  recursive way!

here is what i know about this:

if a function invokes itself and returns the result of this invocation,
this is called tail recursion:

def f(x)
  if x < 0
    return true
  else
    return f(x - 1)
  end
end

the above function is not useful, but it demonstrates tail recursion.
as you see on each function invocation, the program does not need to
store intermediate results to compute the final result, it just returns
whatever the next invocation returns. so, tail recursion is not a
recursion at all! it is just a loop. well, it is a recursion ; -), but
can be implemented without a stack. so the above function can be
rewritten thus:

def f(x)
  while true
  if x < 0
    return true
  else
    x = x - 1
  end
end

hope this helps
konstantin