Cons

In computer programming, cons is a function used by programming languages that are dialects of Lisp. It is the inverse of car and cdr, and is used to construct lists.

For example, to construct the list (apples oranges pears bananas) from the three-element list (oranges pears bananas), you would use cons as follows:

(cons 'apples '(oranges pears bananas))

The function cons always adds the new element to the beginning of the list. It must always have a list to start with, and fortunately, this can be the empty list. As an example, to construct the list (peaches), you would code:

(cons 'peaches ())