[Haskell-beginners] Review request

[C K Kashyap]

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 at 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 at 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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>
>
>
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