User:Eriksiers/Alternate CLISP exponentiation
This is a better example of exponent (it doesn't solve for negatives however so I will leave in tact the other example):
(defun ^ (a b) (let ((r 1)) (dotimes (x b r) (setf r (* r a)))))
(The above example is by Ahungry.)
I wrote this while reading the first few chapters of Practical Common Lisp. (I'm about halfway through chapter 4 right now.) It seems to work -- at least for me, using CLISP -- and I think it might be a better version than the "real" solution provided at Exponentiation operator#Common Lisp, but I'm still way too green to know for sure. (This version can handle negative values of b, whereas that version can't -- I think.)
FWIW, I wrote this before looking at the Exponentiation operator page. Yay me.
Later, I might update this to handle b as a float.
; calculates a to the bth power (a^b) ; b must be an integer ; a can be integer or floating-point ; either or both can be negative ; limits determined by lisp, I suppose -- arbitrary? none? I don't know (defun ^ (a b) (if (> b 0) (* a (^ a (- b 1) ) ) (if (< b 0) (/ 1 (^ a (- 0 b) ) ) (if (= b 0) 1) ) ) )
CL-USER> (^ 1.1 2) 1.21 CL-USER> (^ -1 2) 1 CL-USER> (^ -1 3) -1 CL-USER> (^ -1.1 -1) -0.9090909 CL-USER> (^ 2 300) 2037035976334486086268445688409378161051468393665936250636140449354381299763336706183397376 CL-USER> (^ 1 .5) ; Evaluation aborted on NIL.