Re: [Haskell-beginners] While Condition in Haskell

Hi Lorenzo, what Patrick said was correct. Here's your program a bit more the Haskell way. Also see: http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Data-List... import Data.List main = do let (past, future) = splitAt 8 [4,55,66,77,88,99,12,9,77,88,99,12,-99] subfutures = tail . inits $ future print . takeWhile (`isInfixOf` past) $ subfutures Regards, Thomas On Mon, Oct 11, 2010 at 4:09 AM, Patrick LeBoutillier < patrick.leboutillier@gmail.com> wrote:

Lorenzo,

On Sun, Oct 10, 2010 at 4:15 PM, Lorenzo Isella wrote:

...

... In order to find the length of the longest list in the future which has already been seen in the past, I could select the "true" values in the output of function

iter_find list i

but this is a waste of CPU: I simply would like a while condition to tell my function to stop checking new sublists as soon as it finds one which has not occurred in the past and I would like a counter (a kind of i++) telling me how many times the process has been iterated.

I'm still a beginner myself, but here's my take on it. Since Haskell is lazy, the results will only be generated as they are needed. For example, if you change:

let b = iter_find list i

for

let b = takeWhile id $ iter_find list i

Haskell will stop generating the list as soon as it sees a False result. Then you can take the length of b as your answer.

Patrick

...

Any suggestion is helpful. Cheers

Lorenzo

-------------------------------------------------------------------

import Data.Ord

import Data.List

main :: IO ()

main = do

let list = [4,55,66,77,88,99,12,9,77,88,99,12,-99]

let i = 9

let b = iter_find list i

putStrLn "b is, " print b

is_sublist sublist list = sublist `isInfixOf` list

gen_fut_list list i j = take j $ drop (i-1) list

gen_past_list list i = take (i-1) list

find_in_list list i j = is_sublist (gen_fut_list list i j) (gen_past_list list i)

iter_find list i = map (find_in_list list i) [1..n] where n = (length list) - i +1

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