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Comment by yodelshady | Hacker News Reader

Why on Earth would I want a "zero interval" slice?

It has none of the properties I want in a slice, and that a slice of literally any other length will have. In fact, it means every slice I use needs error-handling, because I might get... something that's functionally not a slice, but is still called one. If that doesn't scream "type error" at you, I don't know what would. In fact, that's precisely why 0 is a comparatively recent invention. Most list-based problems were solved just fine before then.

All these arguments are poor rationalisation for the field's inability to move on from the 8-bit era, where the loss of 1/256 of your address space mattered and compilers had bigger problems to solve than translating indices to offsets.

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You want a zero-slice because it’s a simpler base case in almost any even mildly complex algorithm. Without empty lists, you need many additional branches throughout a code base to handle the “no element” case, causing more potential bugs. There’s nothing “8-bit” about cleaner code, quite the opposite.

No, you have no branches, because the "no element" case is *not a slice! It is a type error at generation!

Instead, I'm dealing with that case at literally every one of thousands of places where I might receive it*! That's not clean.

It is. Just like 0 is a natural number, the empty string is a string, the empty set is a set, etc.

If you've worked with mathematical proofs before, you'll have experience with how they make proofs shorter and more elegant.

That's why they're natural base cases.

Wikipedia says that Egyptians had a 0 as early as 1770 BC - almost 4000 years ago. If that's a "relatively recent" invention, what about computers?

0 comes up if you're doing any arithmetic at all. It's a natural and useful concept for almost anything. As long as you always can take something aways where there is something, you'll need 0. It wouldn't be very useful to make something such as a non-empty list type, to then be able to take away all elements except the last one, which must remain.

In more mathematical terms, 0 is called a neutral element (relative to the addition operation), and almost anything you might want to do (for example subtraction) requires as a consequence a neutral element.

Well, you might want a function which returns String, not Maybe(String), so that you can just concatenate, rather than handle Some(String) or None all the time.

So that's why you might want an empty String. If you have an optional element in a syntax, it can be convenient to match it with a rule using a Kleene star, and that gives you an empty Node, which would return an empty String if you request its value. And so on.

With open intervals, you have to represent that as, say, (3, 2). Which sucks.

Just a friendly correction :-). You have repeatedly confused the meaning of open and closed. "Closed" means including the end element given in the range, and "open" means excluding it.

It may make more sense to think of intervals in the real numbers. "[1,2)" doesn't have a maximum to the right - it has 1.9999....... but not 2. Thus it's "open" to the right. Whereas "[1,2]" includes its maximum (2), so its sealed.

The terms open and closed apply to any set of numbers (not just intervals), where "closed" means that the set includes the limit of any series of numbers in the set, and open means "not closed".

Much appreciated! The terminology and notation seemed backwards to me, and I basically never use it except when discussing Djikstra on HN ;-)

Visually, it looks like ) has more "room" than ], if that makes sense, and that "closed" would mean that the element defines the 'lid' of the range, while "open" means it defines the final extent.

But you can't argue with nomenclature, and extending the definition to the reals helped make it click for me, so I'm unlikely to screw it up again. Thanks!

You could imagine the curved parentheses as "cutting the corner" of the square brackets - or imagine the curve as just gently kissing the endpoint at a single point, while the flat square solidly includes it. "Open" makes sense because it satisfies the criterion that for any number in the interval, you can find a larger (or smaller) number that is also in it - there's "no end".

Literally never wanted that. Had to write thousands of lines of code dealing with that possibility, however, when I could have had a None.

It sucks and is Stockholm syndrome.

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