Emacs Lisp: List

Emacs Lisp's list datatype is an ordered sequence of things. It is known as linked list data structure in computer science. It is an efficient datatype for stack data structure. (like a stack of books, allowing adding or removing one item at a time from the top in an efficient way.)

Lisp list are made up of lower structure called cons, as nested Cons Pair.

Any item can be of any type.

Algorithm properties of lisp list:

• Fast and constant time to get value of first element. (by car)
• Fast and constant time to get rest of list (i.e. without first item). (by cdr)
• Fast and constant time to add one item to the front (beginning of list). (known as push)
• Fast and constant time to remove the first element. (known as pop)
• Any operation for nth element, its time is proportional to size of n.

Create List

• Emacs Lisp: Create List

Empty List, nil

In elisp, empty list is equivalent to nil. The following are all equivalent.

• '()
• (list)
• nil

(eq '() (list ) ) ; t
(eq '() nil); t
(eq (list ) nil ) ; t

Length

length

(length SEQUENCE)

return count of elements.

(equal (length '("a" "b" "c") ) 3)

Get Element from List

• Emacs Lisp: List, Get Elements

Add to List

cons

(cons new list)

Return a new list, with new added to front. (prepend)

(equal
 (cons "a" '("c" "d"))
 '("a" "c" "d"))

(equal
 (cons '("a" "b") '("c" "d"))
 '(("a" "b") "c" "d"))

see also • add-to-list • add-to-ordered-list • push at Emacs Lisp: Modify List

Modify List Variable

• Emacs Lisp: Modify List

Append Join, Convert List

• Emacs Lisp: Join or Convert List, Vector, String

Reference

• Lists (ELISP Manual)