Question

I am new to lisp and am writing a few simple programs to get more familiar with it. One of the things I am doing is writing a recursive and iterative version of a factorial method. However, I have come across a problem and can’t seem to solve it.

I saw a similar error at
Lisp: CHAR is neither declared nor bound
but a solution wasn’t actually reached, other than the OP realized he made a “typing mistake”. In the REPL I can use the setf function and it works fine. I am also using LispBox with emacs. I would appreciate any suggestions!

(defun it-fact(num)
  (setf result 1)
  (dotimes (i num)
    (setf result (* result (+ i 1)))
  )
)

WARNING in IT-FACT :
RESULT is neither declared nor bound,
it will be treated as if it were declared SPECIAL.

Answer 1

You need to bind the variable ‘result’ – using ‘let’, for example – before starting to use it:

(defun it-fact(num)
  (let ((result 1))
    (dotimes (i num)
      (setf result (* result (+ i 1))))))

For futher details you might want to read this …