Re: [css-values] [css-color] XSL-FO and CSS - expression languages compared

> On Nov 17, 2016, at 13:41, Liam R. E. Quin <liam@w3.org> wrote:
> 
> On Thu, 2016-11-17 at 12:11 +0900, Florian Rivoal wrote:
>>> [...]
> 
>>> 
>>> mod (operator)
>>> floor()
>>> ceiling()
>>> round()
>>> min(a, b) - seems better than using units like vmin/vmax
>>> max(a, b)
>>> abs()
>> 
>> [...]
> 
>> in the face of implementation difficulties, it is probably worth
>> looking at specific use cases that would benefit from these, and see
>> if we have other ways of addressing them in CSS. If not, then maybe
>> we should bite the bullet and deal with the complexity.
> 
> Those particular examples aren't non-linear. exp() woud be. mod() is
> non-monatonic, which you might've meant.

It's been a while since I last though seriously about that, but I seem to remember that
as long as we had something which was continuous, piece-wise linear, and strictly monotonic, we were good,
and that breaking any of the three could mean complications.

mod is piecewise linear, but not continuous or monotonic
abs is piecewise linear and continuous, but not monotonic
floor, ceiling, min and max are piecewise linear and continuous, and monotonic but not strictly monotonic
round is piecewise linear but not continuous, and monotonic but not strictly monotonic

I may be misremembering the criteria, and they may not all be of equal difficulty, though. I seem to remember this discussion being raised by dbaron, so maybe he remembers better.

–Florian