From: terje.mathisen@tmsw.no   
      
   EricP wrote:   
   > Terje Mathisen wrote:   
   >> Anton Ertl wrote:   
   >>> Terje Mathisen  writes:   
   >>>   
   >>>> This would have simplified all sorts of array/matrix sw where both   
   >>>> errors (NaN) and missing (None) items are possible.   
   >>>   
   >>> In what ways would None behave differently from SNaN?   
   >>   
   >> It would be transparently ignored in reductions, with zero overhead.   
   >    
   > There is also the behavior with operators - how is it different from xNan?   
   > xNan behaves like an error and poisons any calculation it is in,   
   > which is also how SQL behaves wrt NULL values:   
   >    
   >    value + xNan => xNan   
   >    value * xNan => xNan   
   >    
   > whereas Null is typically thought of as a missing value:   
   >    
   >    value + Null => value?   
   >    value * Null => 0?   
   >    
   > It could also have different operator instruction options that select   
   > different behaviors similar to rounding mode or exception handling bits.   
   > All those option bits would take up a lot of instruction space.   
      
   I'm used to the Mill None, where a store becomes a NOP, a mul behaves    
   like x * 1 (or a NOP), same for other operations.   
      
   Terje   
      
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