diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 33 |
1 files changed, 30 insertions, 3 deletions
@@ -6900,19 +6900,20 @@ A bignum integer: arbitrary precision integer that is heap-allocated. .PP There are additional kinds of objects, such as streams. -.SS Functions null and not +.SS Functions null, not, false .TP Syntax: (null <value>) (not <value>) + (false <value>) .TP Description: -The null and not functions are synonyms. They tests whether <value> is the -object nil. They return t if this is the case, nil otherwise. +The null, not and false functions are synonyms. They tests whether <value> is +the object nil. They return t if this is the case, nil otherwise. .TP Examples: @@ -6920,6 +6921,7 @@ Examples: (null '()) -> t (null nil) -> t (null ()) -> t + (false t) -> nil (if (null x) (format t "x is nil!")) @@ -6927,6 +6929,31 @@ Examples: (if (not (memq 'a list)) (format t "list ~s does not contain the symbol a\en"))) +.SS Function true + +.TP +Syntax: + + (true <value>) + +.TP +Description: + +The true function is the complement of the null, not and false functions. +It return t if the <value> is any object other than nil. If <value> is +nil, it returns nil. + +Note: programs should avoid explicitly testing values with true. +For instance (if x ...) should be favored over (if (true x) ...) + +.TP +Example: + + ;; Compute indices where the list '(1 nil 2 nil 3) has true values: + ;; "Where is (1 nil 2 nil 3) true?" + + [where '(1 nil 2 nil 3) true] -> (1 3) + .SS Functions eq, eql and equal .TP |