[Haskell-beginners] [haskell] About CPS form funtions

[=?GB2312?B?zPC5zw==?=]

Hi,
I am confused by section 4.6 in Yet Another Haskell Tutorial written
by Hal Daume III.
The auther provides a CPS form of "fold" funtion, but I don't know:
1. How to transform a normal function into CPS function. I need some
hint in writting "cfold".
2. Why "cfold" is CPS form? In my mind, if a CPS funtion calls to
other CPS function, it must only feed that function with either direct
variables or continuations. But in the tutorial, cfold defines:
cfold f z l = cfold' (\x t g -> f x (g t)) z l
Note that the lambda function body is f x (g t);  which means call
g(t) first, and take the result, then call f(x, r). It is illegal in
CPS because g(t) will never return. This is not same with function f.
Here, f can be treated as atomic operation (belong the CPS system).

Anyone can help me? Thank you in advance.

---
melon