If !in is inconsistent because of bool/pointer, then so is !

[Daniel Keep]

Rainer Deyke wrote:
> Bill Baxter wrote:
>> Note that D already has things like !>.   But quoth the spec:
>> "For floating point comparison operators, (a !op b)  is *NOT* the same
>> as !(a op b)."
>> [emphasis added]
> 
> I had to check the spec for the difference.  'a !< b' and '!(a < b)'
> /are/ equivalent in the sense that '(a !< b) == !(a < b)' for any values
> of 'a' and 'b'.  The vast majority of the time, the expressions 'a !< b'
> and '!(a < b)' /are/ interchangeable.  The difference is that '!(a < b)'
> sets a global exception state if either operand is NaN, while 'a !< b'
> does not.
> 
> This is, in my opinion, a significant design error in the language.  The
> difference between '!(a < b)' and 'a !< b' is not obvious.  There is
> nothing about the operator '<' that suggests that it should set a global
> exception state, and there is nothing about '!<' that suggests that it
> should /not/ set a global exception state.  (Is global state for error
> reporting ever a good idea in a high-level language?)  It also adds
> awkward expressions to the language, not just in the form '!(a < b)',
> but in the form '!(a !< b)'.

I believe this is, or is the result of, an aspect of IEEE floating point.

  -- Daniel