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| ANSI Common Lisp 17 Sequences 17.3 Dictionary of Sequences
17.3.10 count, count-if, count-if-not | Function
  Syntax: count item sequence `&key` from-end start end key test test-not n count-if predicate sequence `&key` from-end start end key n count-if-not predicate sequence `&key` from-end start end key n Arguments and Values: item - an object. 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 `0` and nil, respectively. key - a designator for a function of one argument, or nil. n - a non-negative integer less than or equal to the length of sequence. Description: count, count-if, and count-if-not 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. Examples:
       (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
Exceptional Situations: Should be prepared to signal an error of type type-error if sequence is not a proper sequence. See Also: Section 17.2 Rules about Test Functions, Section 3.6 Traversal Rules and Side Effects Notes: The `:test-not` argument is deprecated. The function count-if-not is deprecated. Allegro CL Implementation Details: None.

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