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

[Rainer Deyke]

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)'.


-- 
Rainer Deyke - rainerd at eldwood.com