You don't need IO at all for printf debugging. Just call trace or traceShow. https://www.stackage.org/haddock/lts-7.16/base-4.9.0.0/Debug...

Apparently things have changed since 2007... Or else my Ivy league CS professors didn't know what the hell they were talking about. As I grow older and more cynical, the difference between those options continues to narrow...

I wouldn't be surprised at all if Ivy league CS professors didn't have in depth programming knowledge. They are Computer Science professors after all, not programming professors.

If you're teaching a course in X using Y, I don't think it's out of line to expect someone to be proficient in both X and Y. That's kind of their job.

I recently finished a Linux course at school, part of which was focused on Vim. I got points taken away for using gg to jump to the top of a document and G to jump to the bottom. My professor said neither option would work. While I think it is reasonable to expect professors to know what they're talking about, it is fairly common that they don't.

Printf debugging is right there in the prelude: https://hackage.haskell.org/package/base-4.9.1.0/docs/Debug-...