or
Categories: Keywords procedures
, Boolean procedures
;;; (or exp1 exp2 ... expn) : any?
;;; exp1 : expression?
;;; exp2 : expression?
;;; ...
;;; expn : expression?
;;; Evaluate each expression in turn until one of them returns a
;;; truish value (one that is not false). Return that value. If
;;; all of the expressions return false, returns false.
In the special case in which or has no parameters, returns true (#f).
or is a keyword, rather than a procedure. We see the difference primarily in that it has a different evaluation strategy than typical procedures (where we evaluate all the parameters before applying the procedure). Because or is not a procedure, we cannot use it as a parameter to higher-order procedures like map.
> (or #t #f)
#t
> (or #f #t)
#t
> (or #f #f)
#f
> (or #f 3 #t)
3
> (or 3 4 5)
3
> (or 3 (displayln "output") 5)
3
> (or #f (displayln "output") 5)
output
> (or)
#f
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