This section describes functions that accept any kind of sequence.
This function returns
t if object is a list, vector,
string, bool-vector, or char-table,
This function returns the number of elements in sequence. If
sequence is a dotted list, a
wrong-type-argument error is
signaled. Circular lists may cause an infinite loop. For a
char-table, the value returned is always one more than the maximum
Emacs character code.
See Definition of safe-length, for the related function
(length '(1 2 3)) ⇒ 3
(length ()) ⇒ 0
(length "foobar") ⇒ 6
(length [1 2 3]) ⇒ 3
(length (make-bool-vector 5 nil)) ⇒ 5
string-bytes, in Text Representations.
If you need to compute the width of a string on display, you should use
string-width (see Size of Displayed Text), not
length only counts the number of characters, but does not
account for the display width of each character.
This function returns the element of sequence indexed by
index. Legitimate values of index are integers ranging
from 0 up to one less than the length of sequence. If
sequence is a list, out-of-range values behave as for
nth. See Definition of nth. Otherwise, out-of-range values
(elt [1 2 3 4] 2) ⇒ 3
(elt '(1 2 3 4) 2) ⇒ 3
;; We use
stringto show clearly which character
eltreturns. (string (elt "1234" 2)) ⇒ "3"
(elt [1 2 3 4] 4) error→ Args out of range: [1 2 3 4], 4
(elt [1 2 3 4] -1) error→ Args out of range: [1 2 3 4], -1
This function generalizes
aref (see Array Functions) and
nth (see Definition of nth).
This function returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original
sequence, and vice versa. However, the elements of the new
sequence are not copies; they are identical (
eq) to the elements
of the original. Therefore, changes made within these elements, as
found via the copied sequence, are also visible in the original
If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original’s property list. However, the actual values of the properties are shared. See Text Properties.
This function does not work for dotted lists. Trying to copy a circular list may cause an infinite loop.
append in Building Lists,
Creating Strings, and
vconcat in Vector Functions,
for other ways to copy sequences.
(setq bar '(1 2)) ⇒ (1 2)
(setq x (vector 'foo bar)) ⇒ [foo (1 2)]
(setq y (copy-sequence x)) ⇒ [foo (1 2)]
(eq x y) ⇒ nil
(equal x y) ⇒ t
(eq (elt x 1) (elt y 1)) ⇒ t
;; Replacing an element of one sequence. (aset x 0 'quux) x ⇒ [quux (1 2)] y ⇒ [foo (1 2)]
;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x ⇒ [quux (69 2)] y ⇒ [foo (69 2)]