[normaljoe]

> Is there a good reason, other than expectations brought from other langs, why 0 should be falsey?

Most likely this is a result of one of the mother of most bracket based languages specifically C and it's children. BCPL did not have multiple data types which I would guess was an artifact of it's time. I am not certain if this is still the case, but a language that was built in the 60's clearly had limits that are no longer valid. With no types it would be natural to define a boolean as a 0 and 1 in binary which would give you your 0 is falsey.

I was not born yet, and I expect you probably where not as well, when these pivotal decisions where made. It is still interesting to look back and see how what we do today was the result and the why of our forefathers in computer science. For example at the time I can see why Ken Thompson would make the choice of = as assignment instead of := to save bytes and use == for comparison. Assignment being a more often operator would indeed save space, but the amount of bugs it's created since then he probably would not have made that decision.

[kps]

More fundamentally, you want to be able to distinguish the representation(s) of true from false as efficiently as possible, so to work on most machines the choice is either zero vs nonzero or negative vs nonnegative.