Of all the standard Scheme values, only #f counts as false in
conditional expressions. Except for #f, all standard Scheme values,
including #t, pairs, the empty list, symbols, numbers, strings,
vectors, and procedures, count as true.
Boolean constants evaluate to themselves, so they do not need to be quoted in programs.
| not obj | R5RS |
Not returns #t if obj is false, and returns #f otherwise.
(not #t) => #f
(not 3) => #f
(not (list 3)) => #f
(not #f) => #t
(not '()) => #f
(not (list)) => #f
(not 'nil) => #f
|
| boolean? obj | R5RS |
Boolean? returns #t if obj is either #t or #f and returns
#f otherwise.
(boolean? #f) => #t
(boolean? 0) => #f
(boolean? '()) => #f
|