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 |