Arc: Boolean operations

Booleans

Arc provides basic Boolean operations. Only nil and empty list are false; any other value, including 0 and empty string, is true. The operations provide short-circuit evaluation, so only the necessary arguments are evaluated, left-to-right.

See also the Anaphoric operations aand and aor.

no expr Complement: returns true if expr is false, and false if expr is true.	>(no 1) nil >(no nil) t
and [arg ...] The and boolean operator tests if all the arguments are true. It evaluates its arguments in turn until a false argument is found. If all arguments are true, the last argument is returned. If all arguments are false, nil is returned. The and operator performs 'short-circuit' evaluation, and doesn't evaluate arguments that follow a false one.	>(and 1 t 0 "x") "x" >(and nil t) nil >(and nil (/ 1 0)) nil
or [arg ...] The or boolean operator tests if any of the arguments are true. It evaluates its arguments in turn until a true argument is found. If any argument is true, the first true argument is returned. If all arguments are false, nil is returned. The or operator performs 'short-circuit' evaluation, and doesn't evaluate arguments that follow a true one.	>(or nil 42 '() (/ 1 0)) 42 >(or nil '()) nil
nor [arg ...] The nor boolean operator tests if all of the arguments are false. It returns t if all arguments are false, and nil if any arguments are true. It performs 'short-circuit' evaluation, and doesn't evaluate arguments that follow a true one.	>(nor nil nil) t >(nor nil 1 (/ 1 0)) nil

Copyright 2008 Ken Shirriff.