isequal converts ("promotes") both arguments to a common type, if they have
different types. Thus NaN16 and NaN32 are converted to NaN (i.e. NaN64),
hence isequal returns true. See `isequal(5, 5.0)`.
The two equality notions in Julia do nest: `isequal` and `is`, where the
latter is more strict than the former. The operator `==` is basically
identical to `isequal`, except it also handles IEEE semantics, which
technically isn't a valid notion of equality, and thus it cannot nest.
-erik
On Fri, Dec 18, 2015 at 8:09 AM, Tamas Papp <tkp...@gmail.com> 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
>
--
Erik Schnetter <schnet...@gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/
