Generate prime numbers in lisp

p10.lisp

(defun divisible-by (number list)
  "return true if divisible by an element in the list"
  (loop for i in list
       thereis (= (mod number i) 0)))

(defun prime-list-generator (current max-value prime-list)
  "business end of p10"
  (if (= current max-value)
      prime-list
      (if (divisible-by current prime-list)
	  (prime-list-generator (+ current 1) max-value prime-list)
	  (prime-list-generator (+ current 1) max-value (nconc prime-list (list current))))))

(defun p10 (n)
  "Find the sum of all the primes below n"
  (time (reduce #'+ (prime-list-generator 2 n '()))))

(p10 2000000)