From: ThatWouldBeTelling@thevillage.com   
      
   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.   
      
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