Perhaps I've figured at least part of this out; is a combination of view
and decoded going to give me a constant memory conversion from a ByteString
Producer to an MDH Producer? My code now is:
type ErrorResultProducer = P.Producer MDHAndScanLine IO (Either
(P.DecodingError, P.Producer P.ByteString IO ()) ())
measDatMDHScanLinePairs :: Handle ->
IO (Either P.DecodingError ErrorResultProducer)
measDatMDHScanLinePairs h = do
hLen <- P.evalStateT (P.decodeGet getWord32le) (PB.fromHandle h)
case (hLen :: Either P.DecodingError Word32) of
Left err -> return $ Left err
Right len -> fmap Right (skipAndProceed h len)
where
skipAndProceed :: Handle -> Word32 -> IO ErrorResultProducer
skipAndProceed handle l = do
(hSeek handle AbsoluteSeek) (fromIntegral l)
return $ mdhProd (PB.fromHandle handle)
mdhProd :: P.Producer P.ByteString IO () -> ErrorResultProducer
mdhProd bsProd = view P.decoded bsProd
I'm still suspicious of how I'm handling errors here, though. I seem to
have something with several layers of Either, and that must be wrong.
Thanks again,
Dylan
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