[CSC 330] A LISP Starting Point

[Andrew J. Pounds]

Based on conversations I've had today several of you have a lot of 
coding to do to finish off the Happy Numbers project.   It's also 
evident that many of you haven't even cracked open LISP.   While we did 
a simple exercise in class using LISP using arrays,  we did not code the 
prime number finder that we did in several other languages.  I am 
providing you here one I wrote a few minutes ago that uses the same 
"logic" we used in some of the other languages.  I wrote this so it uses 
a main program, a function to print the prime numbers, and a function to 
determine if a number is prime.   It, along with the prior LISP example, 
should provide you a good starting point on your Happy.lisp code.

#!/usr/bin/sbcl --script
;;; Here is the function to print the prime numbers
(defun printprimes (num1 num2)
   (loop for i from num1 to num2 by 1 do
         ( when (isprime i) (print i) )
         )
   (terpri)
   )

;;; Here is the function to determine if a number is prime
(defun isprime ( num )
   (let (( numDivisors 0))
     (loop for i from 1 to num by 1 do
           ( when ( = (mod num i) 0 )
                  ( setf  numDivisors (+ numDivisors 1))
                  )
           )
     ;;; This last function should return true for primes
     (= numDivisors 2)
     )
   )


;;; Here is the main program
(progn
   ;;; Let's define variables to avoid compiler warnings
   (defvar num1)
   (defvar num2)
   (princ "Enter the first number:")
   (terpri)
   (setf num1 (read))
   (princ "Enter the second number:")
   (terpri)
   (setf num2 (read))
   (printprimes num1 num2)
   )


-- 
*/Andrew J. Pounds, Ph.D./*
/Professor of Chemistry and Computer Science/
/Director of the Computational Science Program/
/Mercer University, Macon, GA 31207 (478) 301-5627/
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