Hello, I'm quite new to Haskell, but this is my understanding... Please correct me if I am wrong, as there is a good chance I am. ;) ### Begin Code ### module Main where main = putStrLn (show( (take 4 . map (> 0)) (f s t) )) where s = 2 : t t = 3 : s f = zipWith (-) {- - Output: - *Main> main - [False,True,False,True] -} {- - (take 4 . map (> 0)) (f s t) - Evaluates the list for take until 4 elements have been reached. - Below I replaced (f s t) with the values to make the evaluation - explicit. - - Evaluation: - - map (> 0) (zipWith (-) [2 ..] [3 ..]) - False -- 1st element for take. - - map (> 0) (zipWith (-) [3 ..] [2 ..]) - True -- 2nd element for take. - - map (> 0) (zipWith (-) [2 ..] [3 ..]) - False -- 3rd element for take. - - map (> 0) (zipWith (-) [3 ..] [2 ..]) - True -- 4th element for take. -} -- EOF. ### End Code ### Hope that helps. __ Donnie Jones On Fri, May 9, 2008 at 1:52 PM, PR Stanley <prstanley@ntlworld.com> wrote:
Hi (take 4 . map (>0)) (f s t) where s = 2 : t t = 3 : s f = zipWith (-) What would be the order of evaluation for the above code? How would I illustrate the evaluation step-by-step? I'm guessing that the code necessitates lazy evaluation and as such it starts with take then it applies f which in turn applies s and t and zipWith until the first element satisfies the predicate in map and This is repeated 4 times What does the list think? Many thanks, Paul P.S. I'm not done with induction. I'm just letting it rst for a bit.
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