here is the relevant discussion:
https://github.com/JuliaLang/julia/issues/5314
On Friday, December 18, 2015 at 8:09:10 AM UTC-5, Tamas Papp wrote:
>
> For example,
>
> julia> isequal(NaN,NaN16)
> true
>
> julia> isequal(NaN,NaN32)
> true
>
> This is of course documented in the manual, what I would like to
> understand is the motivation for this design decision. Some languages
> have a progression of equality predicates --- eg Common Lisp has EQ,
> EQL, EQUAL, and EQUALP, each more permissive than the next one. But ==
> and isequal do not nest, since NaN's are of course not == to anything
> under IEEE, even themselves.
>
> Before reading about this in the manual, I thought of isequal as object
> identity ("A and B are equal when they cannot be distinguished"), but
> apparently that's the wrong concept.
>
> Just curious -- there must be a good reason and I would like to know it.
>
> Best,
>
> Tamas
>
