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It's different because #f is a useful value, not a signal that someoperation failed or was invalid.
#f is often used to signal failure. For examples, look no further than string->number and assoc.
In general, operations that are supposed to retrieve a value can fail, and then what value do they return?
Yup, you've identified one of the oldest problems in interface design. Alan -- Dr Alan Watson Centro de Radioastronomía y Astrofísica Universidad Astronómico Nacional de México