OpenEuphoria

Re: Uninitialized Variables

• Posted by Derek Parnell <ddparnell at bigpond.com> Mar 23, 2002
• 437 views

----- Original Message ----- 
From: "Andy Serpa" <renegade at earthling.net>
To: "EUforum" <EUforum at topica.com>
Subject: RE: Uninitialized Variables


> 
> 
> > Apparently NAN is (silly me) Not A Number! :P
> > using equal() compares NAN properly and consistently
> > 
> > Here is my revised uninitialized values for variables:
> > 
> >    integer  = -INF
> >    atom     =  INF
> >    sequence =  NAN
> >    object   = -NAN
> > 
> 
> So how do I test if something is a nan?  The "official" way is to use 
> x!=x, but that is usually optimized away by most compilers (& Euphoria, 
> apparently.)  Using something like if x=1 and x=2 will work in the 
> interpreter, but not translated to C, even with Watcom.  (In fact, it is 
> different depending on the compiler).
> 
> Am I stuck with "if x and compare(x/x,1)"?
> 
> For my genetic programming system this is a very real problem, as it 
> comes up with random mathmatical expressions that sometimes are nan's.  
> If you then take a predicted value (which is a nan) as output for a 
> function that it has created and compare it with a target value, it will 
> show as being equal (& therefore error = 0).  So functions with nan's as 
> output get the highest fitness, which is a disaster...
> 

This seems to work:
--------------
atom x,nan,inf
inf = 1e300 * 1e300
nan = inf / inf

x = nan

if x = nan then
    puts(1, "x is not a number\n")
end if
? x = nan
? x != nan

? nan
? inf
------------