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

[Don]

Daniel Keep wrote:
> 
> 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

Yes. It's the hardware. It's hard to find situations where the 
difference matters.  And this is why !<> and !<>= are the only ones of 
those operators which are actually useful.