length sequence → n

sequence — a proper sequence.

n — a non-negative integer.

Returns the number of elements in sequence.

If sequence is a vector with a fill pointer, the active length as specified by the fill pointer is returned.

(length "abc") → 3 
(setq str (make-array '(3) :element-type 'character 
                           :initial-contents "abc" 
                           :fill-pointer t)) → "abc" 
(length str) → 3 
(setf (fill-pointer str) 2) → 2 
(length str) → 2

Should be prepared to signal an error of type type-error if sequence is not a proper sequence.

list-length, sequence