I recently turned on longlines-mode for my It's All Text buffers as that is generally what I want (especially for this blog). However when I'm editing email for GMail I want to be able to switch between modes as I may be writing a simple message or inserting a patch which shouldn't get mangled.
It took me a bit longer than it should because I was scratching my head trying to work out how to tell if a mode was on. Once I actually read the code it was obvious there is both longlines-mode the variable and (longlines-mode) the function, hence this tweak. I guess it's an idiom enforced by the define-minor-mode macro but I have to admit there is some unfamiliar syntax which I didn't follow. I shall put exploring the elisp macro syntax on my list of things to do once the house is sorted.