> In C, functions are supposed to be idempotent, (without side effects).

What is meant by that statement? Is "idempotent" a mistype/mistakenly selected word? If the author meant "pure" instead, should I file a PR, or consider this some sort of meta-meta-obfuscation? If the author meant "pure", is that actually true of C specifically, or just generally good programming advice (localize side effects to known locations, the fewer the better, don't sprinkle them all over and document where they occur)?