`NotANumber` vs `ArgumentError`

[putianyi889]

Is this behaviour intended? Why is it?

Infinities.jl/test/runtests.jl

Line 41 in 0972ead

@test ∞ - ∞ isa NotANumber

Infinities.jl/test/runtests.jl

Line 163 in 0972ead

@test_throws ArgumentError ∞ + (-∞)

[dlfivefifty]

The second one is because you can't return the result in a type-stable way.

I'm not sure if NotANumber is actually needed anywhere.... if downstream packages pass with an ArgumentError that could be preferable

[putianyi889]

The second one is because you can't return the result in a type-stable way.

That's also a point of #37

I'm not sure if NotANumber is actually needed anywhere

It's discussed in #7

[dlfivefifty]

I'm not sure my argument in #7 holds water as the same would be true for ∞ + (-∞)