No, that's okay, just be aware that I'm not an expert in Haskell and so I'm not going to be 100% sure about answering questions about Haskell's evaluation system.

IO in Haskell is also lazy, unless you use a library for it. So it delays the action of reading in a file as a string until you're actually using it, and in this case that would be when you do some lazy transformations that are also delayed until you use them, and that would be when you're writing them to a file. When you log the transformations, only then do you start actually doing the transformations on the text you read from the file, and only then do you open the file and read a chunk of text from it, like I said.

As for adding a progress bar for the user, there's a question on StackOverflow that asks exactly how to do this, since IO being lazy in Haskell is kind of unintuitive.

https://stackoverflow.com/questions/6668716/haskell-lazy-byt...

The answers include making your own versions of the standard library IO functions that have a progress bar, using a library that handles the progress bar part for you, and reading the file and writing the file in some predefined number of bytes so you can calculate the progress yourself.

But, like the other commenter said, you can also just do things in IO functions directly.

> if the program were running and the system crashed half way through, we'd still have logs for everything that was processed up to the point it crashed

Design choice. This one is all IO and would export logs after every step:

  forM_ entries $ \entry -> do
      (result, logs) <- process entry
      export logs
      handle result