This document discusses functions in LISP. It explains that functions are created using the defun macro, which defines a function name and parameters. The body of the function contains expressions, and the function returns the value of the last expression. Examples are given of defining simple functions to return hardcoded values, add a number, calculate a hypotenuse, and extract characters from a string. The document also provides examples of recursively defining the factorial function in both an iterative and recursive way.

1. CSE240 – Introduction to
Programming Languages
Lecture 19:
Programming with LISP | Functions
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

2. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 2
Function Making
• functions are created by calling a function-making macro. This macro
is called defun.
• the function returns the value of the last expression.
(defun function-name-symbol
(param1 param2 param3 ...)
expr1
expr2
expr3
...
)

3. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 3
Function Making
• (defun do-hello-world ( ) "Hello, World!")
DO-HELLO-WORLD
• (do-hello-world)
"Hello, World!"
• (defun add-four (x) (+ x 4))
ADD-FOUR
• (add-four 7)
11
• (defun hypotenuse (length width)
(sqrt (+ (* length length)(* width width))))
HYPOTENUSE
• (hypotenuse 7 9)
11.4017

4. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 4
Function Making
• (defun first-n-chars (string n reverse-iT)
(if reverse-iT
(subseq (reverse string) 0 n)
(subseq string 0 n)))
FIRST-N-CHARS
• (first-n-chars "hello world" 5 nil)
"hello"
• (first-n-chars "hello world" 5 t)
"dlrow"
• (first-n-chars "hello world" 5 2013)
"dlrow"

5. Test Yourselves

6. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 6
Quiz 1 | Question 1
public static double factorial (double n) {
double sum = 1;
for (double i=0;i < n; i++)
sum = sum * (1 + i);
return sum;
}
public static void main(String [] args) {
System.out.println(factorial(1000)+"");
}

7. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 7
Quiz 1 | Answer 1
(defun factorial (n)
(let ((sum 1))
(dotimes (i n)
(setf sum (* sum (1+ i)))
)
sum
)
)
FACTORIAL
(factorial 1000)
result?
… double factorial (double n) {
double sum = 1;
for (double i=0;i < n; i++)
sum = sum * (1 + i);
return sum;
}
result?

8. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 8
Quiz 1 | Question 2
public static double factorial (double n) {
if (n<=1)
return 1;
else
return n * factorial (n-1);
}
public static void main(String [] args) {
System.out.println(factorial(1000)+"");
}

9. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 9
Quiz 1 | Answer 2
(defun factorial (n)
(if (<= n 0)
1
(* n (factorial (- n 1)))
)
)
FACTORIAL
(factorial 1000)
result?
… double factorial (double n) {
if (n<=1)
return 1;
else
return n * factorial (n-1);
}
result?

10. CSE240 – Introduction to Programming Languages
Javier Gonzalez-Sanchez
javiergs@asu.edu
Fall 2017
Disclaimer. These slides can only be used as study material for the class CSE240 at ASU. They cannot be distributed or used for another purpose.