abstract class $NIL < $IS_NIL |
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**** | Inidicates that the subtype provides a nil value
_ Designer's Note:The advantage of T over SAME is that in parametrized classes typecase e when $NILthen .... e.nil e.nil is now known to be of type T, whereas if it were SAME, you would need at least an extra level of typecase |
$IS_NIL |
$NUMBER{_} | FLT | INT | FLTD |
nil:SAME; |
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