felix winkelmann wrote:
(define sql-null (new-immediate-value))
(define (sql-null? x) (eq? x sql-null))
With the certainty that sql-null won't be eq? to anything else at
all, won't be a list, a record, nothing at all except itself. I
think this could have a few uses.
It would probably have uses, but what would you gain? All you need
is a distinct unique object:
(define sql-null (gensym 'sql-null))
This is still a symbol.
People are using (void) because it's nothing but (void), that is, all
standard predicates (symbol?, pair?, number?, string?...) return #f.
Only its own predicate returns #t.
Tobia
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