Re: [Haskell-cafe] How to deal with last item with concatMapAccumC in Conduit.

I'll preface by saying this probably indicates that the API for concatMapAccumC should be slightly different than it is currently. The problem is that there is no way to convert the final accumulator value into output, and therefore when the input stream ends, that accumulator is simply dropped. One solution (pretty hacky) is to wrap all of the lines in a `Just` and then send in a final `Nothing` value to indicate that the stream is ended. This would look like: https://gist.github.com/snoyberg/6537120fca2e9b8944e41fe60d285793 Another option is to simply use the conduit primitives (await and yield) directly: https://gist.github.com/snoyberg/bd58030db9b9c90f9e1fcf8b31ea10e9 I'd lean towards the latter. On Thu, Jul 20, 2017 at 9:34 AM, jun zhang wrote:

Dear all

the runnable example code is as blow

=================================================================== import Conduit import Text.Regex (matchRegex,mkRegex,Regex)

loghead = mkRegex "^([0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{3} )" -- "2015-01-25 00:04:18,840"

logMerge::Regex->String->String->(String,[String]) logMerge logregex str accum = case matchRegex logregex str of Just _ -> (str,[(accum++"\n")]) Nothing -> case null accum of True -> (str,[]) False -> (accum ++ "<br>" ++ str,[])

runMerge::String->String->IO () runMerge infile outfile = runResourceT $ sourceFile infile $= linesUnboundedC $= concatMapAccumC (logMerge loghead ) "" $$ sinkFile outfile

================================================================

the example input file is --------- 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | errorCode: toString() = null 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | codsexception.getErrorCode(): toString() { errorCode = "UNEXPECTED_PROBLEM" severity = "" } 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | 2015-01-25 00:03:45,331 | DEBUG | WebContainer : 20 | | ---------

the expected output is --------- 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | errorCode: toString() = null 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | codsexception.getErrorCode(): toString() <br>{<br> errorCode =<br>"UNEXPECTED_PROBLEM"<br> severity = ""<br>} 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | 2015-01-25 00:03:45,331 | DEBUG | WebContainer : 20 | | ---------

the actual output is blow, missing the last line of log --------- 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | errorCode: toString() = null 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | codsexception.getErrorCode(): toString() <br>{<br> errorCode =<br>"UNEXPECTED_PROBLEM"<br> severity = ""<br>} 2015-01-25 00:03:44,331 | DEBUG | WebContainer : 20 | | ---------

Thanks

在 2017年7月19日，下午7:50，Michael Snoyman 写道：

I'm afraid I doon't follow what it meant by the stream here. Could you provide a complete, runnable example and indicate what the expected and actual output are?

On Mon, Jul 17, 2017 at 5:48 AM, jun zhang wrote:

...

Dear cafes

I use Conduit to parse a huge file. And I need merge lines by condition.

I find the concatMapAccumC can do that and I write a demo as blow(with conduit-combinators-1.0.6,lts-6.18). The problem is if the last item didn’t make condition true, the data only keep in the accum but missing in stream.

Any one can give me some advises?

Thanks

---------------------------- import Conduit

test'::Int->Int->(Int,[Int]) test' a s = case (a+s) > 5 of True -> (0,[a+s]) False -> (a+s,[])

testlog::IO [Int] testlog = runConduit $ (yieldMany [1,2,3,4,5,6,3]) $= (concatMapAccumC test' 0 ) $$ sinkList

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