zlacker

>>andsoi+(OP)
> "Modern" languages try to avoid exceptions by using sum types and pattern matching plus lots of sugar to make this bearable. I personally dislike both exceptions and its emulation via sum types. ... I personally prefer to make the error state part of the objects: Streams can be in an error state, floats can be NaN and integers should be low(int) if they are invalid.

Special values like NaN are half-assed sum types. The latter give you compiler guarantees.

>>esafak+uTb
Yeah, I'm not sure I've ever seen NaN called or as an example to be emulated before, rather than something people complain about.

>>saghm+pWc
Holy shit, I'd love to see NaN as a proper sum type. That's the way to do it. That would fix everything.

>>echelo+OZc
I suspect that this would result in a lot of .unwrap() calls or equivalent, and people would treat them as line noise and find them annoying.

An approach that I think would have most of the same correctness benefits as a proper sum type while being more ergonomic: Have two float types, one that can represent any float and one that can represent only finite floats. Floating-point operations return a finite float if all operands are of finite-float type, or an arbitrary float if any operand is of arbitrary-float type. If all operands are of finite-float type but the return value is infinity or NaN, the program panics or equivalent.

(A slightly more out-there extension of this idea: The finite-float type also can't represent negative zero. Any operation on finite-float-typed operands that would return negative zero returns positive zero instead. This means that finite floats obey the substitution property, and (as a minor added bonus) can be compared for equality by a simple bitwise comparison. It's possible that this idea is too weird, though, and there might be footguns in the case where you convert a finite float to an arbitrary one.)

>>amelia+DNd
> Have two float types, one that can represent any float and one that can represent only finite floats. Floating-point operations return a finite float if all operands are of finite-float type, or an arbitrary float if any operand is of arbitrary-float type. If all operands are of finite-float type but the return value is infinity or NaN, the program panics or equivalent.

I suppose there's precedent of sorts in signaling NaNs (and NaNs in general, since FPUs need to account for payloads), but I don't know how much software actually makes use of sNaNs/payloads, nor how those features work in GPUs/super-performance-sensitive code.

I also feel that as far as Rust goes, the NonZero<T> types would seem to point towards not using the described finite/arbitrary float scheme as the NonZero<T> types don't implement "regular" arithmetic operations that can result in 0 (there's unsafe unchecked operations and explicit checked operations, but no +/-/etc.).

>>aw1621+Pme
Rust's NonZero basically exists only to enable layout optimizations (e.g., Option<NonZero<usize>> takes up only one word of memory, because the all-zero bit pattern represents None). It's not particularly aiming to be used pervasively to improve correctness.

The key disanalogy between NonZero and the "finite float" idea is that zero comes up all the time in basically every kind of math, so you can't just use NonZero everywhere in your code; you have to constantly deal with the seam converting between the two types, which is the most unwieldy part of the scheme. By contrast, in many programs infinity and NaN are never expected to come up, and if they do it's a bug, so if you're in that situation you can just use the finite-float type throughout.