I did some more refining and I like this one much better - import Text.Regex.Posix start = "<bug>" end = "</bug>" {- s = start encountered e = end encountered ns = new start encountered ne = new encountered -} process s e [] = [] process s e (x:xs) = if ns && not ne then x : process ns ne xs else if ne then [x] else process ns ne xs where ns = if s then s else x =~ start ne = x =~ end main = do str <- readFile "test.txt" let x = process False False (lines str) print (unlines x) On Mon, Jul 16, 2012 at 10:27 PM, Carlos J. G. Duarte < carlos.j.g.duarte@gmail.com> wrote:
I see what you mean. I wasn't aware of the slowness of ++ So your solution is just fine (? asking): you've just made a special takewhile that includes the matching predicate and handled the input like a pipeline. It reminds a Unix command line, in the case: awk '/<bug>/,NR==0' | awk 'NR==1,/<\/bug>/'
On 07/16/12 12:10, C K Kashyap wrote:
Thanks Carlos - you can import Text.Regex.Posix to get (=~) Is there a way to avoid the (++) in your implementation? It has a linear time overhead.
Regards, Kashyap
On Mon, Jul 16, 2012 at 1:36 AM, Carlos J. G. Duarte < carlos.j.g.duarte@gmail.com> wrote:
Looks good to me, but I'm just a beginner! I used the isInfixOf from Data.List instead of =~ to run your example because the later wasn't working on my instalation.
I've made a slightly variant using the break function:
import Data.List
startTag = "<bug>" endTag = "</bug>"
main = interact process
process = unlines . extractSection startTag endTag . lines extractSection start stop xs = let (ls,rs) = break (isInfixOf stop) $ dropWhile (not . isInfixOf start) xs in ls ++ take 1 rs
On 07/15/12 13:08, C K Kashyap wrote:
Hi, I've written a small haskell program to extract a section from a file between start and end markers. For example, if I have a file such as below - a b c <bug> d e f </bug> g h i
I'd like to extract the contents between <bug> and </bug> (including the markers).
startTag = "<bug>"endTag = "</bug>" process = unlines . specialTakeWhile (f endTag) . dropWhile (f startTag) . lines where f t x = not (x =~ t) specialTakeWhile :: (a -> Bool) -> [a] -> [a] specialTakeWhile ff [] = [] specialTakeWhile ff (x:xs) = if ff x then x:(specialTakeWhile ff xs) else [x]
It'll be great if I could get some feedback on this.
Regards,
Kashyap
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