rplaca: [ rē plakϵ ] or [ rϵ plakϵ ]

rplacd: [ rē plakdϵ ] or [ rϵ plakdϵ ] or [ rē plakdē ] or [ rϵ plakdē ]

cons — a cons.

object — an object.

rplaca replaces the car of the cons with object.

rplacd replaces the cdr of the cons with object.

(defparameter *some-list* (list* 'one 'two 'three 'four)) → *some-list* 
*some-list* → (ONE TWO THREE . FOUR) 
(rplaca *some-list* 'uno) → (UNO TWO THREE . FOUR) 
*some-list* → (UNO TWO THREE . FOUR) 
(rplacd (last *some-list*) (list 'IV)) → (THREE IV) 
*some-list* → (UNO TWO THREE IV)

The cons is modified.

Should signal an error of type type-error if cons is not a cons.