On Mon, Dec 8, 2008 at 1:40 PM, 甜瓜
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".
Normal function(s) return value(s). CPS functions take the same value and uses/throws it as a parameter/argument to the "extra" argument, the Continuation. so to transform a function into CPS just 1) make the function take one extra argument, the continuation (the "rest" of the process, next function in chain) 2) instead of returning a value, apply the continuation to the value (call the continuation with the result you would normally return) Example (taken from http://en.wikibooks.org/wiki/Haskell/CPS , check it out) square :: Int -> Int square x = x ^ 2 main = do let x = square 4 print x in CPS : squareCPS :: Int -> (Int -> a) -> a squareCPS x k = k (x ^ 2) main = squareCPS 4 print which shows that here, the print function is the continuation for the square function. instead of returning the value (16, or 4*4 here), the CPS variant feeds the value to the continuation (print here) hope it helps.