Like Streaming.Eversion, but for Producer folds and transformations.

Creating a TransvertibleM out a decoder from Pipes.Text.Encoding. In case the decoding fails, part of the leftovers are read in order to build the error value.

>>> :{
    let trans = transvertM (pipeTransvertibleM (\producer -> do result <- PT.decode (PT.utf8 . PT.eof) producer 
                                                                lift (case result of
                                                                        Left ls -> sample ls >>= lift . throwE
                                                                        Right r -> return r)))
        sample leftovers = L.purely P.fold L.mconcat (void (view (PB.splitAt 5) leftovers))
    in  runExceptT $ L.foldM (trans (L.generalize L.mconcat)) ["decode","this"]
    :}
Right "decodethis"

>>> :{
    let trans = transvertM (pipeTransvertibleM (\producer -> do result <- PT.decode (PT.utf8 . PT.eof) producer 
                                                                lift (case result of
                                                                        Left ls -> sample ls >>= lift . throwE
                                                                        Right r -> return r)))
        sample leftovers = L.purely P.fold L.mconcat (void (view (PB.splitAt 8) leftovers))
    in  runExceptT $ L.foldM (trans (L.generalize L.mconcat)) ["invalid \xc3\x28","sequence"]
    :}
Left "\195(sequen"

Note that the errors are thrown in an ExceptT layer below the Producer and the polymorphic transformer.