I have started to learn Common Lisp a few days ago reading the book from Peter Seibel. I have downloaded the lispbox-0.7 for Windows and tried out some of the concepts in the SLIME REPL.
Now I'm at chapter 7. Macros and Standard Control Structures / Loops and I found this intressting do expression for the 11th Fibonacci number
(do ((n 0 (1+ n))
(cur 0 next)
(next 1 (+ cur next)))
((= 10 n) cur))
I defined following function
(defun fib (n) (do ((i 1 (1+ i)) (cur 0 next) (next 1 (+ cur next))) ((= n i) cur)))
The function does what I expected and returns the nth Fibonacci number. Now for curiosity i tried summing the first 10 fibonacci numbers using a dotimes loop
(let ((sum 0)) (dotimes (k 10) (setf sum (+ sum (fib k)))) sum)
But this expression runs indefinitly and i don't understand why. Maybe here is another concept I don't know. I tried a simpler example like
(dotimes (k 10) (fib k))
which should return NIL. But this also runs indefinitly. Can someone explain to me what I am missing?
Thx
Ok, nevermind, was not carefull enougth. the code tries to evaluate fib 0, but the test condition in do cannot be fulfilled. Thats why it runs indefinitly
fixing it by (fib (+ k 1))