These functions open you up to runtime errors because there are arguments they can't handle (e.g. `head []` -> Exception). I think with a little Haskell experience, "partial function" is familiar enough to not require further explanation.

Each one typically has a safe equivalent: `head` -> `listToMaybe`, `read` -> `reads`, etc but I think the functions and their equivalents are too numerous to mention here.

Implicit in this guideline is not writing your own partial functions as well, not sure if I should make that explicit.