Any attempt to use (a variable set to) NaN for anything, including numerical comparison with anything, including another (variable set to) NaN, or implicitly with either true or false in a conditional statement, should cause an exception.

It is the numerical equivalent of dereferencing a null pointer.

The only tests of NaN that (possibly) should not cause an exception, are for numerical equivalence with a predefined constant NaN, or (perhaps) stringified equivalence to a predefined constant NaN.

Even comparison of one variable set to NaN with another variable set to NaN should raise an exception because to do otherwise would be equivalent to allowing: 

char *a = null, *b = null; 
if( ! strcmp( a, b ) ) {
    printf( "They are the same string\n";
}

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In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: NaNs are true by BrowserUk
in thread NaNs are true by syphilis

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