[Haskell-cafe] Strange error when using Attoparsec and Enumerator

[Crutcher Dunnavant]

Oh thank you!

I can't believe the number of times I read through that code without
seeing that.

On Sun, Dec 5, 2010 at 12:49 PM, John Millikin <jmillikin at gmail.com> wrote:
> I swear attoparsec-enumerator is going to give me grey hair; the error
> you're receiving is because iterParser itself is divergent. Fixed in
> 0.2.0.3, with my sincere apologies.
>
> On Sun, Dec 5, 2010 at 09:14, Crutcher Dunnavant <crutcher at gmail.com> wrote:
>> I have spent a good chunk of the past week tracing code, trying to
>> solve this problem. I'm seeing an error when using Enumerator and
>> Attoparsec that I can't explain. This is a reduced form of the
>> problem.
>>
>> In general, I've observed that debugging broken iterators and
>> enumerators is very hard. We probably want some tooling around that;
>> I'm looking at an identity enumeratee with debug.trace shoved in, or
>> something like that, not sure yet what would help.
>>
>> {-
>> Haskell 2010, ghc 6.12.3
>> array-0.3.0.2
>> attoparsec-0.8.2.0
>> attoparsec-enumerator-0.2.0.2
>> bytestring-0.9.1.7
>> containers-0.4.0.0
>> deepseq-1.1.0.2
>> enumerator-0.4.2
>> text-0.10.0.0
>> transformers-0.2.2.0
>> -}
>> import Control.Applicative ((<|>))
>> import qualified Data.Attoparsec.Char8 as AP
>> import qualified Data.Attoparsec.Combinator as APC
>> import qualified Data.Attoparsec.Enumerator as APE
>> import qualified Data.ByteString.Char8 as B
>> import qualified Data.Enumerator as E
>> import Data.Enumerator (($$))
>> import System.IO as IO
>>
>> parseLine :: AP.Parser B.ByteString
>> parseLine = do
>>  AP.char '+'
>>  return . B.pack =<< APC.manyTill AP.anyChar endOfLineOrInput
>>
>> endOfLineOrInput :: AP.Parser ()
>> endOfLineOrInput = AP.endOfInput <|> AP.endOfLine
>>
>> pp :: Show a => AP.Parser a -> String -> IO ()
>> pp p s = do
>>  result <- E.run $
>>    E.enumList 1 [ B.pack s ]
>>    $$ E.sequence (APE.iterParser p)
>>    $$ E.printChunks False
>>  case result of
>>    (Right _) -> return ()
>>    (Left e)  -> IO.hPutStrLn stderr $ show e
>>
>> main = pp parseLine "+OK"
>> {-
>> Observed output:
>> ["OK"]
>> *** Exception: enumEOF: divergent iteratee
>>
>> Problems with this:
>> 1) I didn't write an iteratee, enumerator, or enumeratee in this code.
>> Something's wrong.
>>
>> 2) If the parser is divergent, I _should_ be getting the error message:
>>  "iterParser: divergent parser"
>> -}
>>
>> --
>> Crutcher Dunnavant <crutcher at gmail.com>
>>
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>



-- 
Crutcher Dunnavant <crutcher at gmail.com>