My goal is to parse a big text-file line by line using the same parser for every line. I am new to Conduit and I've read this https://www.fpcomplete.com/user/chad/snippets/random-code-snippets/folding-l ines-in-conduit article. After adding import Control.Monad.Trans.Resource for runResourceT and adding rankNTypes, I got it working. Code in www.tbsoftware.nl/TestConduit/TestConduit7.hs I don't understand what is going on in myFunc. Does CL.fold fold over the already read lines? I wonder whether CL.fold loads the whole file in memory? if I change count <- CL.fold (\count t -> count + T.length t) 0 to count <- CL.fold (\count t -> T.length t) 0 nothing changes in the output. If count is always zero, why using a fold? How can I get the 'current line' in myFunc? Kees