1. Arrays (1) You create an array in LISP by using the function (make- array ). All elements are initially set to nil. To create a 1-dimensional array of size 3 (make-array 3) To create a 2-dimensional array of size 3 x 3 (make-array ‘(3 3)) To create a 3-dimensional array of size 3 x 3 x 3 (make-array ‘(3 3 3)) Array index always starts from 0.

2. Arrays (2) In the previous examples, after you have created the arrays, there was no way by which you could refer to it. Here is how you can assign an array to a variable: (setq an_array (make-array 3)) How would you then set and access the values of each cell within an array?

3. Aref… To access a particular element in an array, use a function called aref. For example, if you have a 1 dimensional array named an_array 10 elements, then to access the nth element, you could do this: (aref an_array n) For example: (aref an_array 9) (aref an_array 7)

4. Setf Setf is the only way to set the elements of an array. To set the nth element of an_array to a particular value, do as follows: (setf (aref an_array n) value) For example (setf (aref an_array 5) “Hello”)

5. Incf …(an interesting function?) Incf reads a NUMBER from an array at a specified position, increments it, and then writes it back. Assume an_array = #(“hello” NIL 3) Then (incf (aref an_array 2)) will give you #(“hello” NIL 4) What happens if you do this: (incf (aref an_array 0)) (incf (aref an_array 1))