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> Somewhat interestingly, it detects it and SIGABRTs, which technically isn't a segfault. And that's now some black magic that I'm curious about as I really thought it would have segfaulted.

It's a signal handler, of course: https://github.com/rust-lang/rust/blob/d8bdb3fdcbd88eb16e1a6...

> I think it is fair to call C "unsafe" given the above definition of safe/unsafe.

I don't think anyone would disagree with this. What they're saying is that a segfault is safe and that's because a segfault is essentially your OS's version of an out-of-bounds error, one of the reasons that C is not safe is because an out-of-bounds access will not necessarily cause a segfault.

> such as (1/0).foo.foo (and yes you need the second .foo…)

I don't understand the nuance here. In my Firefox developer tools, I can do the following:

> (1/0).foo.foo

---> TypeError: (intermediate value).foo is undefined

> (1/0).foo

---> undefined

> (1/1).foo.foo

---> TypeError: 1.foo is undefined

> Infinity.foo.foo

---> TypeError: Infinity.foo is undefined

> undefined.foo

---> TypeError: undefined has no properties

While these are all different errors, I don't really understand why the '(1/0).foo.foo' case is an example of a _trapped_ error, but the others are not.

The point they were making is that (1/0).foo is not an error, as it returns a value.

None of those are trapped errors.

In Python, Java, C, OCaml, and most other languages, 1 / 0 aborts the program. That is, division by zero is a trapped error.

In JavaScript, it's not. It keeps going and lets you do stuff like access nonexistent properties .foo on the result, which are also untrapped errors.

So JavaScript is unsafe in Cardelli's terminology. It gives you untrapped errors rather than trapped ones. The program keeps chugging along until you find out later and have to trace backwards to the bug.

It's Infinity in Haskell

    Prelude> 1.0 / 0.0 :: Double
    Infinity

Because / is floating point division, and infinity is a defined value in floating point numbers.

Try it again with div for integer division.

Thanks, removed.

I’m sort of surprised by that since my memory is that infinity isn’t a real number, rational, etc. That is, does infinity in Haskell obey some algebraic laws?

Infinity is a valid floating point number in the ISO standard.

However integer division by 0 isn’t. div 1 0 will fail.

Yeah it's an interesting case. It appears that Inf is in floating point to AVOID a trapped error.

This answer has an interesting way of looking at it. If you go on the theory that floating points are supposed to represent reals, then in floating point, you can't tell if a value is actually zero or just indistinguishably close to zero.

In the case of "indistinguishably close to zero", you're getting the wrong answer, and the program doesn't halt. It keeps on chugging doing bad math. So that's an untrapped error, and it's UNSAFE by Cardelli's definition.

https://cs.stackexchange.com/questions/82811/why-do-floating...

The key point is that "safe" sometimes means "crashes" and sometimes means "doesn't crash". It's an auto-antonym in that sense.

A broader definition is "errors are flagged as early as possible", including with seg faults / hardware exceptions.

Floats aren’t reals, at best they are an approximation for certain calculations. +0 and -0 are defined and distinct floating point numbers. Floating point math is known to be problematic and does not evenly distribute numbers on the real line either. There are numerical methods used for reducing error on floating point operations when it is acceptable. Otherwise fixed point or intervals may be used.

This is false. Integer division by zero is undefined, but floating point division is perfectly fine. Many languages have different operators to distinguish floating point and integer division, like pythons / for floats and // for integers.