sequence—a proper sequence.
predicate—a designator for a function of one argument that returns a generalized boolean.
from-end—a generalized boolean. The default is false.
test—a designator for a function of two arguments that returns a generalized boolean.
test-not—a designator for a function of two arguments that returns a generalized boolean.
start, end—bounding index designators of sequence.
The defaults for start and end are
key—a designator for a function of one argument,
n—a non-negative integer less than or equal to the length of sequence.
count and return the number of elements in
the sequence bounded by start and end
that satisfy the test.
The from-end has no direct effect on the result. However, if from-end is true, the elements of sequence will be supplied as arguments to the test, test-not, and key in reverse order, which may change the side-effects, if any, of those functions.
(count #\a "how many A's are there in here?") → 2 (count-if-not #'oddp '((1) (2) (3) (4)) :key #'car) → 2 (count-if #'upper-case-p "The Crying of Lot 49" :start 4) → 2
Should be prepared to signal an error of type
sequence is not a proper sequence.
Section 17.2 (Rules about Test Functions), Section 3.6 (Traversal Rules and Side Effects)
The :test-not argument is deprecated.
count-if-not is deprecated.