— Function: car cons-cell

This function returns the value pointed to by the first pointer of the cons cell cons-cell. Expressed another way, this function returns the car of cons-cell.

As a special case, if cons-cell is nil, then car is defined to return nil; therefore, any list is a valid argument for car. An error is signaled if the argument is not a cons cell or nil.

          (car '(a b c))
               ⇒ a
          (car '())
               ⇒ nil

— Function: cdr cons-cell

This function returns the value pointed to by the second pointer of the cons cell cons-cell. Expressed another way, this function returns the cdr of cons-cell.

As a special case, if cons-cell is nil, then cdr is defined to return nil; therefore, any list is a valid argument for cdr. An error is signaled if the argument is not a cons cell or nil.

          (cdr '(a b c))
               ⇒ (b c)
          (cdr '())
               ⇒ nil

— Function: car-safe object

This function lets you take the car of a cons cell while avoiding errors for other data types. It returns the car of object if object is a cons cell, nil otherwise. This is in contrast to car, which signals an error if object is not a list.

          (car-safe object)
          ==
          (let ((x object))
            (if (consp x)
                (car x)
              nil))

— Function: cdr-safe object

This function lets you take the cdr of a cons cell while avoiding errors for other data types. It returns the cdr of object if object is a cons cell, nil otherwise. This is in contrast to cdr, which signals an error if object is not a list.

          (cdr-safe object)
          ==
          (let ((x object))
            (if (consp x)
                (cdr x)
              nil))

— Function: nth n list

This function returns the nth element of list. Elements are numbered starting with zero, so the car of list is element number zero. If the length of list is n or less, the value is nil.

If n is negative, nth returns the first element of list.

          (nth 2 '(1 2 3 4))
               ⇒ 3
          (nth 10 '(1 2 3 4))
               ⇒ nil
          (nth -3 '(1 2 3 4))
               ⇒ 1
          
          (nth n x) == (car (nthcdr n x))

— Function: nthcdr n list

This function returns the nth cdr of list. In other words, it removes the first n links of list and returns what follows.

If n is zero or negative, nthcdr returns all of list. If the length of list is n or less, nthcdr returns nil.

          (nthcdr 1 '(1 2 3 4))
               ⇒ (2 3 4)
          (nthcdr 10 '(1 2 3 4))
               ⇒ nil
          (nthcdr -3 '(1 2 3 4))
               ⇒ (1 2 3 4)

— Function: caar cons-cell
— Function: cadr cons-cell
— Function: cdar cons-cell
— Function: cddr cons-cell
— Function: caaar cons-cell
— Function: caadr cons-cell
— Function: cadar cons-cell
— Function: caddr cons-cell
— Function: cdaar cons-cell
— Function: cdadr cons-cell
— Function: cddar cons-cell
— Function: cdddr cons-cell
— Function: caaaar cons-cell
— Function: caaadr cons-cell
— Function: caadar cons-cell
— Function: caaddr cons-cell
— Function: cadaar cons-cell
— Function: cadadr cons-cell
— Function: caddar cons-cell
— Function: cadddr cons-cell
— Function: cdaaar cons-cell
— Function: cdaadr cons-cell
— Function: cdadar cons-cell
— Function: cdaddr cons-cell
— Function: cddaar cons-cell
— Function: cddadr cons-cell
— Function: cdddar cons-cell
— Function: cddddr cons-cell

Each of these functions is equivalent to one or more applications of car and/or cdr. For example,

          (cadr x)

is equivalent to

          (car (cdr x))

and

          (cdaddr x)

is equivalent to

          (cdr (car (cdr (cdr x))))

That is to say, read the a's and d's from right to left and apply a car or cdr for each a or d found, respectively.

— Function: first list

This is equivalent to (nth 0 list), i.e. the first element of list. (Note that this is also equivalent to car.)

— Function: second list

This is equivalent to (nth 1 list), i.e. the second element of list.

— Function: third list
— Function: fourth list
— Function: fifth list
— Function: sixth list
— Function: seventh list
— Function: eighth list
— Function: ninth list
— Function: tenth list

These are equivalent to (nth 2 list) through (nth 9 list) respectively, i.e. the third through tenth elements of list.