Checks whether the predicate is true for every element combination
Supported Platforms: Windows and Mac OS
(vl-every predicate-function list [list ...])
Type: Subroutine or Symbol
The test function. This can be any function that accepts as many arguments as there are lists provided with vl-every, and returns T on any user-specified condition. The predicate-function value can take one of the following forms:
Type: List
A list to be tested.
Type: T or nil
T, if predicate-function returns a non-nil value for every element combination; otherwise nil.
Thevl-every function passes the first element of each supplied list as an argument to the test function, followed by the next element from each list, and so on. Evaluation stops as soon as one of the lists runs out.
Check whether there are any empty files in the current directory:
(vl-every '(lambda (fnm) (> (vl-file-size fnm) 0)) (vl-directory-files nil nil 1)) T
Check whether the list of numbers in nlst is ordered by '<=:
(setq nlst (list 0 2 pi pi 4)) (0 2 3.14159 3.14159 4) (vl-every '<= nlst (cdr nlst)) T
Compare the results of the following expressions:
(vl-every '= '(1 2) '(1 3)) nil (vl-every '= '(1 2) '(1 2 3)) T
The first expression returned nil because vl-every compared the second element in each list and they were not numerically equal. The second expression returned T because vl-every stopped comparing elements after it had processed all the elements in the shorter list (1 2), at which point the lists were numerically equal. If the end of a list is reached, vl-every returns a non-nil value.
The following example demonstrates the result when vl-every evaluates one list that contains integer elements and another list that is nil:
(setq alist (list 1 2 3 4)) (1 2 3 4) (setq junk nil) nil (vl-every '= junk alist) T
The return value is T because vl-every responds to the nil list as if it has reached the end of the list (even though the predicate has not yet been applied to any elements). And since the end of a list has been reached, vl-every returns a non-nil value.