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64.3.5 The category ‘nonnegative’

The category of nonnegatives are those comparables which are not less than zero. This explicitly implies, that 0 is nonnegative. The restriction to comparables is necessary, since the membership is indeed tested as in the definition.

The category's predicate is nonnegativep.

— Function: nonnegativep object

Return t if object is a nonnegative number, nil otherwise.

We call a number object non-negative iff it is comparable and its value is not less than 0. 

     (nonnegativep 0)
          ⇒ t
     (nonnegativep 1/2)
          ⇒ t
     (nonnegativep 1.5)
          ⇒ t
     
     (nonnegativep -1/2)
          ⇒ nil
     (nonnegativep -0.5)
          ⇒ nil
     
     (nonnegativep 1+2i)
          ⇒ nil